Treating process

(54) (56) (57)

PATENT INVENTOR INVENTOR'S OFFICE NAME

Tioxide Group plc, London GB

Ian Livsey, Sedgefield GB, Rachael Louise Parry, Yarm GB AB Stockholm Patent Office, Zacco & Bruhn Coating process of an inorganic powder by polymerization using ultrasound

CALLED PUBLICATIONS:

EP Al 0 054 832 (C08F 2/44), GB A 1,340,045 (C09C 1/36), GB A 1,369,468 (C08F 2/44)

SUMMARY:

Process of coating or encapsulating an inorganic powder is described, wherein the powder, preferably a pigment, is dispersed in an aqueous medium and an ethylenically unsaturated monomer is polymerized in the presence of the powder while subjecting the reaction mixture to ultrasonic vibrations. The monomer is present in an amount not exceeding 200% by weight of the powder, and is preferably an acrylate or methacrylate.

The powder carries a cationic charge on its surface and can be generated by treating the surface with preferably an aluminum salt.

The numbers mom parentheses indicate international identification code, INID code. Letters in clamps indicate international document code.

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The present invention relates to a treatment procedure and in particular to the treatment of an inorganic powder with organic material.

According to the invention, a process for treating inorganic powder is included by polymerizing a reaction mixture with an ethylenically unsaturated monomer in the presence of a dispersed inorganic powder with cationic charge on the surface of the corresponding particles, the monomer being present in an amount not exceeding 200% by weight of the powder. together with the treatment of the monomers and the powder by ultrasonic waves at least during some part of the polymerization with the specified monomer, in a manner in which the particles are coated with polymerized monomer.

The object of the invention relates to a method for coating particles based on inorganic powder with organic polymer. By the process, the entire amount of free polymer formed and not included as part of the coating is minimized, and apparently the resulting coating becomes thicker than a coating obtained by a method which does not involve the use of ultrasonic waves. The products are well dispersed and aggregate formation is minimized.

In general terms, the process relates to the preparation at the initial stage of a dispersion, normally an aqueous dispersion of the inorganic powder to be coated, and, if necessary, modification of the corresponding particles so that the surface of the particles will support a cation charge. An ethylenically unsaturated monomer is then normally added to the dispersion with the inorganic powder and the polymerization is started by suitable method. During at least some of the polymerization, the dispersion with the inorganic powder is subjected to ultrasonic waves, which advantageously act in the manner indicated. In order to minimize further formation of free polymer monomer is obtained. the length does not exceed 200% by weight of the inorganic powder.

The present process can be used in the coating of particles with optional inorganic powder, however, the inorganic pigments, diluents and fillers are of greater interest. Most useful, especially the inorganic pigments have been found to be and the pigments in question refer to titanium 508 764 dioxide pigments, alumina pigments, antimony oxides, barium pigments, calcium pigments, zirconium pigments, chromium pigments, iron pigments and magnesium pigments. Extender and / or fillers such as silica, silicates, aluminates and especially clays may also be treated by the present process. Pigment mixtures and extenders can also be treated and likewise non-pigmented forms of the inorganic powders referred to as pigments in this context. According to a particularly preferred process, the inorganic powder is titanium dioxide pigment, preferably rutile titanium dioxide. The inorganic powder may advantageously have a finely divided form for the coating, and, if necessary, painting may be carried out with suitable apparatus to achieve this condition.

In the polymerization, the dispersed inorganic

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sate of lyra. However, in the case of a plurality of the inorganic powders, it is necessary to take a real treatment with a surface charge modifier.

In a large number of cases, the dispersion with the inorganic powder can be treated with suitable cations and such cations may for example refer to Al⁺, Zn ^⁺, Th4⁺, U02 ^⁺ as well as Pd2⁺. However, the use of aluminum salts is preferred in view of the low cost of the ion and the size of the ion.

Preferably, starting from mineral acid, for example aluminum sulphate or aluminum chloride.

However, the salt agent is partially replaced or used in conjunction with an organic compound which is cationic in the specific dispersion. If necessary, the organic compound as such may be a polymerizable monomer, however non-polymerizable cationic compounds may be used. Preferably, the organic compound is a polyelectrolyte and suitable compounds may be protein colloids, cationic guar gum, certain polymers based on methacrylates, vinylamine and vinyl pyridine.

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Methacrylic acid can be added to the powder dispersion, normally before the surface modifier as a supplementary additive, when desired.

The amount of surface charge modifier need only be sufficient to give the intended cationic charge density and can be readily determined by electrophoresis or other methods. Commonly present amounts of the surface charge modifier are between 2.5% by weight and 7.5% by weight of, for example, an aluminum salt, on the basis of the amount of inorganic powder, depending on the specific inorganic powder to be treated with the intended cationic charge.

As will be apparent from the context, the present process involves the polymerization of an ethylenically unsaturated monomer for coating inorganic powder particles with polymer or copolymer as needed. All ethylenically unsaturated monomers which are polymerizable in emulsion polymerization systems can be used according to the invention. Normally, the polymer produced is preferably insoluble in water, and if required, it can be crosslinked by suitable crosslinking agent. For example, ethylenically unsaturated monomers are aliphatic or aromatic compounds containing a polymerizable unsaturated group such as the unsaturated carboxylic acids or unsaturated carboxylic esters. One of the carbon atoms forming the double bond may preferably carry two hydrogen atoms and this type of compound may be referred to as vinyl monomers. Examples of useful monomers include acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid or the corresponding anhydride, fumaric acid and crotonic acid. Esters of acid monomers can be used such as methyl acrylate, ethyl acrylate, methyl methacrylate, butyl acrylate and ethyl methacrylate. Other monomers that can be polymerized in the preparation of coatings include styrene, vinyl toluene, alphamethylstyrene, ethylene, vinyl acetate, vinyl chloride, acrylonitrile, etc.

If necessary, two or more of the polymerizable monomers can be copolymerized. Bridging agents may also be included, and examples of the substances may be mentioned di- or

508 764 polyfunctional ethylenically unsaturated monomers such as ethylene glycol dimethacrylate, ethylene glycol diacrylate, allyl methacrylate,

1,3-butanediol dimethacrylate.

The amount of crosslinking agent in question may be in the range of 10 to 50% by weight of the substance based on the total amount of monomer used.

It should be apparent from the context that the amount of the polymerizable ethylenically unsaturated monomer does not exceed

200 % by weight of the inorganic powder and preferably the amount is not greater than 100% by weight.

In a particularly preferred process, the amount of the polymerizable ethylenically unsaturated monomer is in the range of 2% to 25% by weight of the inorganic powder.

Initially, the inorganic powder may normally form an aqueous dispersion, if necessary through the action of a dispersant. The dispersion may optionally be ground and then incorporated into the dispersion any of the surface modifiers required, which is accompanied by or preceded by any type of organic polyelectrolyte or other additive. Since the additive is an organic acid such as methacrylic acid, a certain amount of cross-linking agent, for example ethylene glycol dimethacrylate, can also be added.

In the present process, prior to mixing with inorganic powder, the selected monomer is normally allowed to form a single 11 emulsion, where necessary a non-ionic or anionic emulsifier or equivalent mixture is used to assist in the emulsification. As emulsifiers may be mentioned sodium dodecylbenzenesulfonate and ethoxylated alkylphenols, for example those wherein the alkyl group is a nonyl, octyl or decyl substituent. Other known emulsifiers may be used.

If the polymerization is intended to take place in the presence of a cross-linking agent intended for the selected ethylenically unsaturated monomer or monomers, it is normally but not always incorporated into the inorganic powder separate from the monomer emulsion.

Normally, the polymerization is initiated by a water-soluble initiator such as a peroxy compound, a persulfate, a peracetate or a redox initiator, e.g., a salt of a persulfuric acid.

508 764 or an organic hydroperoxide or peroxide together with a sulfite, bisulfite, hydrosulfite or metal formaldehyde sulfoxylate.

The initiator is added at any suitable step, for example, prior to incorporation of the monomer with the inorganic powder. Only a portion of the initiator amount required can first be added, followed by the remaining required amount or amounts at two or more subsequent steps.

The polymerization of the added monomers is normally carried out at elevated temperature and depending on ambient temperature in the range of 25 ° C to 60 ° C, normally between 30 ° C and 50 ° C. The polymerization is normally carried out but not always in an inert atmosphere, for example under a protective atmosphere or an inert gas, for example nitrogen.

In the present process, at least the polymerization is allowed to take place partly because the mixture of monomer and inorganic powder is subjected to the influence of ultrasonic waves. Usually this is achieved by immersing an ultrasonic vibrator in the aqueous mixture which is polymerized, and preferably the vibrations are allowed to affect the mixture from the beginning of the polymerization. The ultrasonic vibrations include network-based ultrasound, usually based on frequencies in the range of 50 kHz. The effect that is actually transferred to the mixture depends in part on the volume, and it has been found that the most advantageous results are obtained by using ultrasonic vibrations with relatively low effects. Preferably, the output power of the polymerization mixture is in the range of 15 to 60 watts per liter of blend and especially 20 to 30 watts per liter. Normally, an amount of the inorganic powder in the mixture is used in the range of 150 to 300 g per liter, preferably 200 to 240 g per liter.

The use of ultrasonic vibrations with less power value results in homogeneous coating based on the degree of coverage taken into account. Higher power values ​​result in improved dispersion of the particles of the inorganic powder. The use of inorganic powder at lower levels in the aqueous dispersion also results in improved thickness and homogeneity of the coating.

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The coated particles obtained by the present process can be used as coating pigments in paints and other media such as in plastics and inks. The coating results in the dispersion of the inorganic material being improved in organic media and also tends to reduce the abrasive effect of the powder on fabrication units intended for plastics and containing the powders.

The invention is illustrated by the examples which follow.

EXAMPLE 1

The process of preparing coated inorganic powders is broadly described by the numbered steps indicated, during which dry nitrogen atmosphere was maintained in the reaction vessel. Step 1

Inorganic powder (&lt;190 g) was weighed into a 1 liter metal vessel and 750 ml of distilled water washed with N 2 &lt;30-60 min dry N 2&gt; was added. The slurry was mechanically stirred at 20 ° C for 5-10 minutes.

step 2

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

Step 3

ACN (2.8 g) (AIN) was added and stirring 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 min). Stirring was continued at 40 ° C for 15 minutes.

Step 5

Fresh solutions with 1% potassium persulfate &lt;0.265 g / 25 ml, solution A) and 1% sodium bisulfite &lt;0.25 g / 25 ml, solution B) were prepared. 1.8 g of solution A and 0.9 g of solution B were incorporated into the metal vessel and stirring continued for 15 minutes. Step 6

Methyl methacrylate (MMA, 7.5 g) was emulsified in water (100 ml) with an emulsifier (EA) &lt;0.38 g) using an ultrasonic probe (&lt;5 minutes). The emulsion was added (&lt;5 ml equal parts) with stirring over the 15 minute period.

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Step 7

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

Step 8

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

Step 9

After 4 hours, the product was filtered, washed with water and dried for 1 day at 70 ° C.

The emulsifier was isooctylphenoxy polyethoxyethanol and was commercially available under the trade name Triton-X.

In the specific experiments that were carried out as described in more detail below, the reaction vessel was, based on experiment 2, subjected to ultrasound through an ultrasonic bath (10-lO / cm 2 watts) and for the remaining experiments by ultrasonic probes with different starting fundamental effects. one with the maximum rated output value 225 watts (probe X) and one with the maximum rated output value 375 watts (probe Y). The ultrasound was used according to three different programs, ie

Program

<td>IN</td><td>- during</td><td>steps</td><td> 1</td><td>t</td><td>O</td><td>m</td><td> 5</td>

<td>E</td><td>- during</td><td>steps</td><td> 1</td><td>t</td><td>O</td><td>m</td><td> 7</td>

<td>P</td><td>- during</td><td>steps</td><td> 5</td><td>t</td><td>O</td><td>m</td><td> 7</td>

Twenty-six experiments were carried out in the manner described as follows under the conditions shown in Table 1. The combined wattages constituted the respective amount of power to which the reactants were exposed in connection with the probe being in operation. In trials 3 to 8, 11 to 18 and 21 to 26, the probe operated at 30% of graduated baseline and in the other trials at 60% of graded baseline. The indicated reactant values ​​refer to those shown in the main assembly (ie, 1 = the same; 14 = H of the main assembly value, etc.).

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<td colspan="3"></td><td colspan="2">CHART</td><td colspan="4"> 1</td>

<td></td><td>ENLARGE</td><td>ULTRASONIC SOUND / WATT / STAY TIME</td><td>POWDER</td><td>MA</td><td>A1N</td><td>EDMA</td><td>EA</td><td>MMA</td>

<td> 5</td><td> 1</td><td>NONE</td><td>1 B 2 SO,</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td></td><td> 2</td><td>BATH / WATTS / E</td><td>1 Ba₂SE₄</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td></td><td> 3</td><td>Y / 47 / C</td><td>in Tio₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td></td><td> 4</td><td>X / 28 / P</td><td>in Tio₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 10</td><td> 5</td><td>Y / 47 / E</td><td>alkylthio₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td></td><td> 6</td><td>X / 28 / E</td><td>alkylthio₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td></td><td> 7</td><td>X / 28 / I</td><td>alkylthio₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 15</td><td> 8</td><td>Y / 47 / I</td><td>alkylthio₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

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

<td></td><td> 10</td><td>Y / 41 / E</td><td>alkylthio₂</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td></td><td> 11</td><td>Y / 22 / E</td><td>1 TiO₂</td><td> 1</td><td> 1</td><td> 1</td><td>y₂</td><td> 1</td>

<td> 20</td><td> 12</td><td>X / 28 / E</td><td>1 TiO₂</td><td> 1</td><td> 1</td><td> 1</td><td>y₂</td><td> 1</td>

<td></td><td> 13</td><td>Y / 22 / I</td><td> ’/₂Ten₂</td><td> ½</td><td>y₂</td><td>y₂</td><td>y₂</td><td>y₂</td>

<td></td><td> 14</td><td>X / 28 / I</td><td> &gt;/₂Ten₂</td><td>V2</td><td>Ϋ2</td><td>y₂</td><td>y₂</td><td>y₂</td>

<td></td><td> 15</td><td>Y / 22 / I</td><td> ‘/₂Ten₂</td><td> 1</td><td> 1</td><td> 1</td><td>y₂</td><td> 1</td>

<td> 25</td><td> 16</td><td>X / 28 / I</td><td>y₂Ten₂</td><td> 1</td><td> 1</td><td> 1</td><td>y₂</td><td> 1</td>

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

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

<td rowspan="2"> 30</td><td> 19</td><td>Y / 41 / I</td><td>y₂Ten₂</td><td> 1</td><td> 1</td><td> 1</td><td>y₂</td><td> 1</td>

<td> 20</td><td>X / 55 / I</td><td>V2TaO₂</td><td> 1</td><td> 1</td><td> 1</td><td>y₂</td><td> 1</td>

<td></td><td> 21</td><td>Y / 22 / I</td><td>1T1O₂</td><td> 2</td><td> 2</td><td> 2</td><td> 1</td><td> 2</td>

<td></td><td> 22</td><td>X / 28 / I</td><td>alkylthio₂</td><td> 2</td><td> 2</td><td> 2</td><td> 1</td><td> 2</td>

<td> 35</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></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></td><td> 25</td><td>Y / 22 / I</td><td>alkylthio₂</td><td> 2</td><td> 1</td><td>l (DVB)</td><td>y₂</td><td> 1</td>

<td></td><td> 26</td><td>X / 28 / I</td><td>1 TiO₂</td><td> 2</td><td> 1</td><td>l (DVB)</td><td>y₂</td><td> 1</td>

<td> 40</td><td>DVB =</td><td>divinylbenzene i</td><td>instead</td><td>for</td><td>EDMA</td><td></td><td></td><td></td>

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The obtained products were examined with electron microscope and the photomicrographs were assessed visually. The study mainly showed that ultrasound use led to an improvement in the coverage of the product according to experiment 2 compared to experiment 1.

It was determined that the most favorable effect was obtained when the ultrasound was used only at the initial stage of the reaction, i.e., I surpassed P which surpassed E.

Even the use of lower power levels led to improved coverage compared to higher power, but higher power levels, however, caused better dispersion of the coated particles.

An increase in the emulsifier / powder ratio led to improved coverage. A decrease in TiO2^-the content resulted in a slight improvement in the thickness and homogeneity of the coating. Likewise, increased monomer content caused increased coverage and homogeneity of the coating.

In the tests, the ten oxide used was an amount extracted from the reactor obtained by steam phase oxidation of titanium tetrachloride.

EXAMPLE 2

The procedure described in more detail in Example 1 was repeated with certain deviations, which are more detailed in the experimental description that follows. The probe was for probe Y and the power was supplied in the form of the input value 22 watts at steps 1 through 5 unless otherwise indicated. The powder used was titanium dioxide as in experiments 3 to 26.

Attempt 27

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

Try 28

Three different amounts of emulsifier (EA) were used which corresponded to 5% by weight, 3% by weight and 12% by weight of monomer one.

In all cases, corresponding coating grades were obtained on the powder, however, the optimum level corresponded to about 10% by weight of monomer.

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Attempt 29

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

Try 30

The styrene was used in place of methyl methacrylate. The product exhibited uniform polymeric coating.

Trial 31

A mixture of equal weight amounts of methyl methacrylate and butyl acrylate was used instead of methyl methacrylate alone. The product obtained a homogeneous polymer coating.

Try 32

Methyl methacrylate was replaced with butyl methacrylate. An encapsulated product was obtained.

Try 33

As emulsifier (EA), sodium dodecylbenzenesulfonate is used. A coated product was obtained, however, the coating thickness was not the same as that obtained from the emulsifiers of experiments 1 to 24.

Try 34

Cetyl trimethylammonium bromide was used as an emulsifier. A product equivalent to that of Experiment 33 was obtained. Try 35

As the emulsifier, sodium dodecylbenzenesulfonate is used, and butyl acrylate is used instead of methyl methacrylate. A homogeneously coated product was obtained.

Try 36

Methyl methacrylate amounts were selected corresponding to 1%, 3%, 5%,

<td> 7%,</td><td> 9%,</td><td> 11%, 13%, 15%,</td><td> 17%, 19%,</td><td> 21% ,</td><td>23% and 25% polymer count</td>

<td>sodium</td><td>on</td><td>powder weight. IN</td><td>every</td><td>case</td><td>coated product was obtained</td>

<td>best.</td><td></td><td></td><td></td><td></td><td></td>

<td colspan="2">Attempt</td><td> 37</td><td></td><td></td><td></td>

Potassium persulfate in the amounts of 1%, 2%, 3%, 4%, 5%, 6% and 6.5% of the powder weight is used and sodium metabisulfite in the amounts of 1%, 2%, 3% and 3.25% based on the powder is used. at steps 5 and Θ. Polymer-coated products were obtained consistently with optimum coating in connection with the use of potassium persulfate in the amounts 1.44% and 6.5% in steps 5 and Θ, respectively, and sodium metabisulfite in the amounts 0.72% and 3.25% in steps 5 and Θ, respectively.

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Try 38

A mixture of 2 parts by weight of styrene and one part by weight of methyl methacrylate was used instead of methyl methacrylate. As a product, polymer coated powder was obtained.

Try 39

The sound vibrations were introduced at all reaction steps, however, according to a pulsation scheme (at the approximate intervals of 20 seconds) instead of continuous operation. In this case too, a polymer coated product was obtained. Try 40

The procedure of Example 1 was performed except that the input power at step 1 was 50 watts. A polymer coated powder was obtained.

In cases where Examples 27 to 40 replace a reactant (or mixture) with another reactant described in Example 1, the corresponding weight amount of the substituted substance is used unless otherwise indicated.

All products were analyzed visually by transmission electron micrograph in.

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