GB2241958A - Powder treatment process - Google Patents

Abstract

A process for the treatment of a water-insoluble powder involves polymerising ethylenically unsaturated monomer onto the powder surface employing gamma ray radiation to initiate the polymerisation. Preferably the powder is titanium dioxide and the source of gamma rays is Cobalt-60. The treated powders are usable in paints and other products where a high degree of resistance to weathering is required.

Description

FORMAL SPECIFICATION TREATMENT PROCESS This invention relates to a novel treatment process and particularly to a new process of encapsulating particulate solids especially titanium dioxide.

It is an object of the present invention to provide a better procedure for manufacture of new materials for use in paints, plastics, composites, heterogeneous catalysts, friction and lubricating products, and use in separation and analytical procedures and other technical applications.

A further object of this invention is to coating powders with fluorine-containing polymers which impart to solid materials unique chemical and physical properties hardly achievable by other means.

A further object of the present invention is to provide coatings, including fluorinated systems for photo- and chemically active pigments, e.g. titania, for use in paint formulations to improve organophilicity and dispersibility of pigment, eventually oil repelling hydrophobicity and other characteristics of final paints, and for retarding degradation of organic matrices by preventing diffusion of water and other polar molecules along the active inorganic surfaces.

A still further object of this invention is to provide basic encapsulated material covered by polymers with reactive functional groups, e.g. poly(methacryloyl chloride), for another chemical modification and preparation of laminated and composite material of new types.

According to the present invention a process for the treatment of a powder comprises forming a mixture of an ethylenically unsaturated monomer and a water-insoluble powder particles and subjecting the mixture to gamma ray irradiation to initiate polymerisation of said monomer and form a coating of polymerised monomer on said powder particles.

As described in the process of the present invention there is polymerised an ethylenically unsaturated monomer to coat waterinsoluble powder particles with a polymer or copolymer as is desired.

Any ethylenically unsaturated monomer which is polymerisable by gamma radiation can be used in the present invention. Usually the polymer produced desirably is insoluble in water and, if necessary may be cross-linked by a suitable cross-linking agent. Typical ethylenically unsaturated monomers are aliphatic or aromatic compounds containing a polymerisable unsaturated group such as the unsaturated carboxylic acids or unsaturated carboxylic acid esters. One of the carbon atoms forming the double bond can preferably carry two hydrogen atoms and such compounds would be named vinyl monomers. Typical monomers useful are acidic monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid or its anhydride, fumaric acid or crotonic acid.

Esters of acid monomer can be used such as methyl acrylate, ethyl acrylate, methyl methacrylate, butyl acrylate and ethyl methacrylate.

Other monomers which can be polymerised to form coatings are styrene, vinyl toluene, alpha methylstyrene, ethylene, vinyl acetate, vinyl chloride, acrylonitrile, and the like.

Ethylenically unsaturated fluorinated monomers can also be used to produce the products of the invention. Typical fluorinated monomers include aliphatic or aromatic compounds containing polymerisable ethylenically unsaturated groups, such as unsaturated carboxylic acid esters containing fluorine atoms as part of the ester function. One of the carbon atoms forming the double bond preferably carries fluorine atoms and fluoroalkyl substitutes and such compounds are those named fluorinated vinyl monomers. Typical specific monomers include fluorinated alkenes, fluorinated ethers, fluorinated acrylic and methacrylic acids and fluorinated esters of acid monomers such as fluorinated methacrylates, fluorinated acrylates and fluorinated heterocyclic compounds.

If desired the polymer coating can be a copolymer of two or more of the polymerisable monomers. The polymer coating can be cross linked and typical cross-linking agents which can be used are difunctional ethylenically unsaturated monomers, for example ethylene glycol dimethacrylate, ethylene glycol diacrylate, allyl acrylate, 1,3butanediol diacrylate, divinyl benzene or 1,3-butanediol dimethacrylate.

The amount of the cross-linking agent can be in the range of 10% to 50% by weight on total weight of monomers employed.

The amount of said polymerisable ethylenically unsaturated monomer is usually not greater than 200% by weight of the powder and preferably the amount is not greater than 100% by weight. In the most desirable process the amount of said polymerisable ethylenically unsaturated monomer is within the range 2% to 25% by weight of the inorganic powder.

The process of the present invention can be used to coat the particles of any water-insoluble powder but those of more interest are the inorganic pigments, extenders and fillers. Particularly, inorganic pigments are found to be of most use in the process and such pigments are titanium dioxide pigments, aluminium oxide pigments, antimony oxides, a zinc oxide pigment, barium pigments, calcium pigments, zirconium pigments, chromium pigments, iron pigments and magnesium pigments. Extenders and/or fillers such as silica, silicates, aluminates and particularly the clays can also be treated by the process of the invention. Mixtures of pigments and extenders can also be treated as well as non-pigmentary forms of the inorganic powders mentioned as pigments. In the most preferred process the inorganic powder is titanium dioxide pigment, preferably rutile titanium dioxide.Desirably the inorganic powder is ir, a finely divided state prior to coating and, if necessary, can be milled by suitable means to achieve such a state. An example of an organic powder is cellulose powder.

Encapsulation or coating of the powdered solid material according to the present invention can be generally performed with suspensions of the solids in solutions of the reacting monomers and other additives in suitable solvents, by exposing to gamma ray radiation The powder can be predispersed in the reaction medium with the aid of a dispersion agent, which can be, in certain cases, the monomer itself or a suitable comonomer e.g. acrylic or methacrylic acid or glycerol methacrylate. Suitable solvents for encapsulation are those which are unreactive (inert) and in which the organic components (monomers etc) are sufficiently soluble, and the use of volatile, nonflammable, nontoxic and regenerable solvents are preferable.The best results, from this point of view, are achieved with fluorinated solvents, which have been found to be partly included in the encapsulated product and thus do improve some of the final properties of the coated material. A typical fluorinated solvent is 1, 1,2-trichloro-trifluoroethane.

Any suitable source of gamma radiation can be used and Cobalt60 is a suitable source of gamma rays for this process. The suspensions to be irradiated may contain different ratios of solid materials, organic reagents and solvents according to their chemical reactivity and the purpose of coating. To obtain a homogeneous coating layer it is important to have efficient agitation during the whole reaction which can be achieved mechanically or by application of ultra-sound.

Inhibitors seem to have no substantial effect on the end results, but removing them from monomers just before the reaction, is desirable, as is degassing or purging of the reaction mixture by inert gas.

The total amounts of radiation received by the reaction mixture depends on the particular materials being treated and also on the amounts being used. Total amounts within the range of 15M rads to 0.5M rads are generally used and preferably from 6M rads to 1M rads.

Products of the present invention find use in a wide variety of products and services as set out previously hereinbefore. Paints and other products in which a high resistance to weathering is required are ideal uses.

The following Examples illustrate the invention.

In these Examples when the encapsulation of pigmentary titania is described it was carried by using a rutile titanium dioxide pigment, obtained via sulphate route which had a specific surface area of 10 m2 per gram, (which corresponds to an average particle diameter of 0.1 um). All other reagents were reagent or technical grade and used as received without further purification. Monomer inhibitors were not removed. 1,1,2-Trichloro-trifluoroethane was generally used as the solvent.

All grafting, encapsulation and coating experiments were performed in sealed Pyrex Carius tubes of approximately 100 ml capacity by following this procedure:- about 5g of solid powdered material (2g in the case of glass or cotton fibres) were slurried in the reaction tube with 20-30 mt of 1,1,2-trichlorotrifluoroethane containing usually methacrylic acid and after the addition of liquid monomer or in the case of gaseous monomers via vacuum transfer, the contents of the tube were degassed in a 3 freeze-thaw cycles and the tube with the reactants frozen (liquid air) was sealed under vacuum The ampoule was then placed on a Carius tube holder, fastened to the motor of a slow running motor and exposed to the gamma irradiation at a distance of 18 cm, using the a cobalt-60 gamma ray source.The total radiation dose at a rate of (21.5 k rad/h) received by the ampoules was calculated using the Fricke dosimeter. The ampoules were opened while the contents were frozen (liquid air) and after warming to laboratory temperature the products were isolated by filtration, dried at approximately 700 and atmospheric pressure for several hours, and examined usually by infrared spectroscopy, electron microscopy or, in certain cases, by electron spectroscopy for chemical analysis. The infrared specifia were recorded using thin KBr pellets (d = 15 mm) and a Perkin-Elmer 577 Grating Infrared Specterphotometer.

EXAMPLE 1 100 parts (4.75g) of titanium dioxide powder was slurried with 663 parts by weight (20 ml) of trichlorotrifluoroethane solution containing 10 parts (0.48g) of methacrylic acid and after the addition of 21 parts (1.0g) of trifluoroethyl methacrylate the reaction mixture was degassed and exposed to gamma irradiation of 2.117 M rad total radiation dose whilst being continuously agitated. On completion of the procedure the coated titania was isolated by filtration, dried at 70O and atmospheric pressure and examined by infrared spectroscopy, electron microscopy and electron spectroscopy for chemical analysis. 1176 parts (5.6g) of fully encapsulated material was obtained which displayed strong hydrophobicity being exposed to water.

EXAMPLE 2 100 parts (5g) of finely divided titanium dioxide was slurried with 630 parts (20 ml) of trichlorotrifluoroethane solution containing 3 parts (0.15g) of methacrylic acid and after the addition of 12 parts (0.60g) of methyl methacrylate the process was accomplished following the procedure described in Example 1 using the radiation dose of 3.144 M rad.

109 parts (5.46g) of thin coated material was obtained which contained by electron spectroscopy about 14% of trichlorotrifluoroethylene in the polymer coating layer. The material was well dispersible in hydrophilic solvents.

EXAMPLE 3 To the 100 parts (5g) suspension of titanium dioxide in 630 parts (20 ml) of trichlorotrifluoroethane solution containing 4 parts (02g) of methacrylic acid was added 12 parts (0.6g) of pentadecafluorooctylmethacrylate and the procedure was accomplished as described in EXample 1 with the total irradiation dose 1.584 M rad.

The 108 parts (5.4g) of thin coated titania was obtained which displayed or very strong surface active properties in contact with water, being uniformly dispersed on the surface and with a tendency to form unwetted beads or distorted surface forms. In water it was dispersible only with the aid of an organic surfactant.

EXAMPLE 4 15 parts (0.75g) of methacrylic acid inhibited with 1000 ppm hydroquinone and 250 ppm hydroquinone monomethyl ether was dissolved in 630 parts (20 ml) of trichiorofluoroethane and after the addition of 100 parts (5g) of dry titania powder the reaction mixture was degassed and exposed to the 2.064 M rad total radiation dose.

112 parts (5.66g) of relatively thick and uniform coated materials was isolated, which was readily dispersible in water, giving a system with a milky appearance.

EXAMPLE 5 The suspension of 100 parts (5g) of titanium dioxide powder, 3 parts (0.15g) of methacrylic acid and 630 parts (20 nix) trichlorotrifluoroethylene was thoroughly mixed in a heavy walled glass ampoule and 31 parts (1.57g) of gaseous chlorotrifluoroethylene was vacuum transferred to the degassed and frozen suspension. After sealing the ampoule, the reaction mixture was irradiated with gamma rays (2.064 M rad does). The ampoule was opened and he product was isolated by filtration and dried at 70O under atmospheric pressure and characterised by infrared spectroscopy, electron microscopy and electron spectroscopy.

The 109 parts (5.46g) of a thin coated powdered material was obtained.

EXAMPLE 6 The 100 parts (5g) of titanium dioxide were slurried with 630 parts (20 ml) of trichlorotrifluoroethane solution containing 3 parts (0.15g) of methacrylic acid, thoroughly mixed in a heavy walled glass ampoule of approximately 100 ml internal capacity, and 18 parts (0.92g) of gaseous 1,1-difluoroethylene was vacuum transferred into the degassed and frozen reaction mixture. After gamma irradiation (2.064 M rad does) the product was isolated and characterized following procedure described in Example 5.

The 112 parts (5.59g) of fully encapsulated titania was obtained, which displayed hydrophobicity and regular dispersity on the water surface.

EXAMPLE 12 To the dispersion of 500 parts (5.0g) of titanium dioxide in 630 parts (20 ml) trichlorotrifluoroethylene was added 20 parts (lg) of glycidyl methacrylate and the degassed reaction mixture was exposed to 2.139 M rad does of gamma rays being slow agitated and worked up as described in Example 1.

110 parts (55g) of coated titania was obtained.

EXAMPLE 13 Procedure described in the above Example 12 was repeated with the same solvent containing 4 parts (0.2g) of methacrylic acid and with 1.910 M rad dose of gamma irradiation.

112 parts (6.1g) of dry fully encapsulated material was obtained.

EXAMPLE 14 100 parts (5g) of zinc oxide powder was slurried with 630 parts (20 ml) of trichlorotrifluoroethane containing 4 parts (0.2g) of methacrylic acid and 20 parts (1.0g) of trifluoroethyl methacrylate was added to the reaction mixture, which, after degassing, was irradiated by 2.139 M rad dose of gamma rays and agitated. 112 parts (5.6g) of well encapsulated hydrophobic pigment was isolated following the procedure of the Example 1.

EXAMPLE 15 100 parts (5g) of cellulose powder was mixed with 630 parts (20 ml) of trichlorotriflyoroethane solvent containing 4 parts (0.2g) of methacrylic acid and with 20 parts (1.or) of trifluoroethyl methacrylate.

The reaction mixture was degassed and exposed to 1.597 M rad dose of gamma rays being agitated.

110 parts (55g) of hydrophobic powdered material was obtained following the procedure of the Example 1.

EXAMPLE 16 100 parts (5g) of aluminium oxide powder was slurried with 630 parts (20 ml) trichlorotrifluoroethane solvent containing 4 parts (0.2g) of methacrylic acid and after the addition of 20 parts (1.0g) of trifluoroethyl methacrylate the reaction mixture was degassed and irradiated by 1.597 M rad dose of gamma rays whilst being agitated.

The reaction mixture was washed up as described in previous Examples and 120 parts (6g) of modified slightly brown coloured aluminium powder was obtained.

EXAMPLE 17 100 parts (5g) of titania powder was slurried with 630 parts (20 ml) trichlorotrifluoroethane solvent containing 4 parts (0.2g) of methacrylic acid, shaken up and 20 parts (1.0g) of iscyltrimethylsilane were added. Thus obtained reaction mixture was degassed and irradiated by 1.910 M rad dose of gamma rays. 104 parts (5.2g) of dry modified hydrophobic material was isolated after filtration.

Claims (31)

1. A process for the treatment of a powder comprising forming a mixture of an ethylenically unsaturated monomer and water-insoluble powder particles and subjecting the mixture to gamma ray irradiation to initiate polymerisation of said monomer and form a coating of polymerised monomer on said powder particles.

2. A process according to claim 1 in which the ethylenically unsaturated monomer is a vinyl monomer.

3. A process according to claim 1 or 2 in which the monomer contains a carboxylic acid group or a carboxylic ester group.

4. A process according to claim 1, 2 or 3 in which the monomer is acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid or crotonic acid.

5. A process according to claim 1, 2 or 3 in which the monomer is methyl acrylate, ethyl acrylate, methyl methacrylate, butyl acrylate or ethyl methacrylate.

6. A process according to claim 1 in which the monomer is styrene, vinyl toluene, alpha-methylstyrene, ethylene, vinyl acetate, vinyl chloride or acrylonitrile.

7. A process according to claim 1 in which the monomer is an ethylenically unsaturated fluorinated monomer.

8. A process according to claim 7 in which the monomer is an unsaturated carboxylic acid ester containing fluorine in the ester function

9. A process according to claim 7 in which the monomer is a fluorinated vinyl monomer.

10. A process according to claim 7 in which the monomer is a fluorinated alkene, a fluorinated acrylic acid, a fluorinated methacrylic acid, a fluorinated methacrylate, a fluorinated acrylate or a fluorinated heterocylic conmpound.

11. A process according to any one of the preceding claims in which a mixture of two or more of said monomers are co-polymerised.

12. A process according to any one of the preceding claims in which the mixture includes a cross-linking agent for said polymerised monomer.

13. A process according to claim 12 in which the cross-linking agent is a difunctional ethylenically unsaturated monomer.

14. A process according to claim 13 in which the cross-linking agent is ethylene glycol dimethacrylate, ethylene glycol diacrylate, allyl acrylate, 1,3 butanediol diacrylate, divinyl benzene, or 1,3 butanediol dimethacrylate.

15. A process according to claim 12, 23 or 14 in which the amount of the cross-linking agent is from 10% to 50% by weight of the total weight of monomers.

16. A process according to claim 1 in which the monomer is such as to produce on polymerisation poly(methacryloyl chloride).

17. A process according to any one of the preceding claims in which the total amount of said monomer is not greater than 200% by weight of said powder.

18. A process according to claim 17 in which the amount is not greater than 100% by weight.

19. A process according to claim 18 in which the amount is from 2% to 25% by weight.

20. A process according to any one of the preceding claims in which the said powder is an inorganic pigment, an extender or a filler.

21. A process according to claim 20 in which the pigment is a titanium dioxide pigment.

22. A process according to claim 20 in which the pigment is an aluminium oxide pigment, an antimony oxide pigment, a zinc oxide pigment, a barium pigment, a calcium pigment, a zirconium pigment, a chromium pigment, an iron pigment or an magnesium pigment.

23. A process according to claim 20 in which a silica, a silicate or an aluminate forms the extender or filler.

24. A process accoding to any one of the preceding claims in which the total amount of gamma ray radiation received by the mixture is from 15M rads to 0.5M rads.

25. A process according to claim 24 in which the total amount of radiation received is from 6M rads to 1M rads.

26. A process according to any one of the preceding claims in which the gamma ray radiation is provided by a Cobalt 60 source.

27. A process according to any one of the preceding claims in which the monomer is dissolved in a solvent therefor in which the powder is dispersed.

28. A process according to claim 27 in which the solvent is a fluorinated solvent.

29. A process according to claim 28 in which the solvent is 1,1,2 trichloro-trifiuorethane.

30. A process for treating a powder according to claim 1 substantially as described in any one of the foregoing Examples.

31. A treated powder when prepared by a process according to any one of the preceding claims.