CA2024460A1 - Polymer-encapsulated platelet-like substrates - Google Patents

Abstract

Abstract Polymer-encapsulated platelet-like substrates, obtainable by polymerization of an organic monomer system which contains platelet-like substrates which have been sur-face-modified using organic coupling agents, are eminen-tly suitable for use in formulations such as paints, dye compositions and plastics.

Description

- 2Q2~0 Merck Patent Gesellschaft mit beschrànkter Haftung 6100 Darmstadt Polymer-encapsulated platelet-like substrates The in~ention rQlates to polymer-encapsulated platelet-like substrates obtainable by polymerization of an organic monomer system which contains platelet-like substrates which have been surface-modified using organic coupling agents.

Platelet-like substrates i.e. materials having a rela-tively small thickness in relation to length and width are u~ed in many fields of technology. For in~tance, platelet-like minerals such as, for example, kaolin, mica or talc are used in finely divided form as fillers for plastics. Platelet-like pigments such as, for example, metal oxide-coated mica platelets or platelet-like iron oxide or bismuth oxychloride are used not only in the pigmenting of, for example, paints, colorants, plastics and the like but al~o in cQsmetic preparations.

The ever increasing utility of platelet-like substrates in different industrial fields increasingly requires the development of surface-modified ~ubstrates to ultimately ensure the compatibility of the substrate~ with further components present in industrial compositions.

A fundamental problem is the strong tendency of platelet-like substrates of this type to form agglomerates in which the substrates are present lying on top of one another like a deck or house of cards and can only bs separated again with difficulty owing to strong adhesion.
This is all the more troublesome since on incorporating platelet-like sub~trates in formulations, high shear forces cannot be applied owing to the fragility of the thin substrates.

2~ 6 0 Numerous methods have therefore been developed, inter alia, to solve the problem of incorporating platelet-like pigments, in particular, into thermoplastic materials (DE-A-2,603,211, DE-A-3,221,044, DE-A-3,627,329).

Furthermore, coatings have been disclosed which contain polysiloxanes for improved weather resistance (DE 3,334,598) or silicones (EP 0,224,978). However, these processes are either too expensive or the coated pigments have only a restricted use.

The treatment of platelet-like substrates with coupling agentssuch as organotitanates for improved dispersibility in cosmetic preparations and with organosilanes for improved water resistance hasbe2n disclosed (EP 0,306,056 or EP 0,268,918), but polymer-encapsulated substrates have not been disclosed.

Ths ob~ect of the present invention was to provide im-proved processes for the polymer coating of platelet-like substrates. In particular, the substrates must be com-patible in a great many different industrial formulations without losing the typical properties of platelet-like substrates. There is a need, inter alia, for platelet-like, ~urface-modified pigment~ which can be incorporated without Io8s of their pigment properties into formu-lation~. ~xamples of frequently occurring disadvantages with pigment incorporation are pigment shock, i.e. the formation of agglomerates on incorporation owing to incompatibilities, and pigment migration.

This ob~ect is achieved by the present invention. In particular, it has been found that platelet-like ~ub-strates can be readily encapsulated with polymer systemsif they have previously been treated with organic cou-pling agents.

The present invention accordingly provides polymer-` ` 2~244~

encapsulated platelet-like ~ubstrates obtainable by polymerization of an organic monomer system which con-tains platelet-like subRtrates which have been surface-modified using organic coupling agents.

In particular, the invention provide~ latex systems which contain the substrates according to the invention.

The invention also provides a procass for the preparation of latex sy3tems of this type, which is characterized in that platelet-like substrate~ are treated with organic coupling agents which ara suitable for hydrophobizing the substrate particles, and tho substrates which have been modified in this manner are finely distributed in an aqueous solution with the addition of an emulsifier, this giving micelle-like structures, and to this dispersion is added a monomer and optionally an initiator, and the monomer system is polymerized.

Finally, the invention provides the use of the platelet-like substrates which have been surface-modified using or~anic coupling agents or of the latex systems which contain substrates of this type, in paints, dye compo-sitions and plastics.

The invention ultimately provides formulations which contain the substrates or latex systems according to the inv~ntion.

Preferred platelet-like substrates for surface modifica-tion according to the invention are, in particular, layer-structured silicates and oxides or oxide-coated materials, since these have reactive OH groups on their surface. Example~ of these are, on the one hand, mica, talc, kaolin or other comparable minerals and, on the other hand, also platelst-like iron oxide, bismuth oxychloride and the metal oxide-coated micas known as pearl lustre pigments, and also aluminium platelets and 2~2~

oxide-coated aluminium platelets. All conventional pearl lustre pigments can be used, for example mica coatings containing coloured or colourless met~l oxides such as rio2, Fe2O3, SnO2, CrzO3, ZnO and other metal oxides as ~uch or mixed in a uniform layer or in succes~ive layers.
These pigments have been di~closed, for example, in the German Patents and Patent Applications 1,467,468, 1,959,998, 2,009,566, 2,214,545, 2,215,191, 2,244,298, 2,313,331, 2,522,572, 3,137,808, 3,137,809, 3,151,343, 3,151,354, 3,151,355, 3,211,602 and 3,235,017. Further-more, the abovementioned platelet-like substrates may also be coated with organic dye compositions or pigment molecules.

The coupling agents used can be appropriate compounds as described, for example in the following publications:

Edwin P. Plueddemann; Silane Coupling Agents; Plenum Press; New York, London (1982) and the literature referred to therein. Salvatore J. Monte, Gerald Sugerman;
Ken-React Reference Nanual - Titanate, Zirconate and Aluminate Coupling Agents (1987~ and the literature referred to therein. Dynasilan Haftvermittler, Organo-funktionelle Silane, Technische Information Dynamit Nobel (1985). Lawrence B. Cohen, The Chemistry of Zirson-aluminate Coupling Agents and their Application in HIgh Solids Coatings, ~ater-borne and Higher-Solids Coatings Sympoaium, New Orleans 1986. Lawrence B. Cohen, Corro~ion Reduction in High Solids an Water-borne Coating~ using Zirconaluminate Adhesion Promoters, Water-borne and Higher-Solids Coatings Symposium, New Orleans, 1988.
Peter Z. Moles, The Application of Zirconium Compounds in Surface Coatings, Water-borne and Higher-Solids Coatings Symposium, New Orleans, 1987.

As a rule, cuitable compounds contain one or more metal centre~ such as Si, Ti, Zr or Al to which functional organic group~ are bonded. Examples of suitable silanes ~ 2 ~ 0 are the commercially available DYNASYLAN~ agents (Dynamit Nobel)~ These are alkoxysilane derivatives having two or three alkoxy radicals and one or two alkyl radicals to which additional functional groups may also be bonded, for example amino, mercapto~me~cryloxy or a nitrile group or a halogen radical such as chlorine. Examples of ~uitable titanate coupling agents are the commercially available "RR~ or "~ICA~ materials (Renrich Petrochemicals, Inc.).
Like the abovementioned silanes, these agents are com-pounds having alkoxy radical~ and, optionally, additionalradicals ~ubstituted by functional groups, the radicals of the said compounds being bonded via oxygen to the metal centre. Examples of the functional groups are amino, mercapto or hydroxyl groups.

Examples of suitable zirconate coupling agents are the compounds obtainable from Renrich Petrochemicals, Inc.
under the designation "RZ n or ~LZ n agents, these com-pounds, if appropriate, having amino or mercapto groups.
Furthermore, the substrates according to the invention can be prepared using zirconium aluminates ~uch as, for example, the appropriate "Cavco Mod~ agents obtainable from Cavedon Chemical Co., Inc. Polymer encapsulations according to the invention using zirconium aluminates as coupling agents can, in particular, also be suitably carried out using platelet-like metal substrates, for example platelets of Al, Cu or Zn or alloys.
The coupling agents are applied either directly or by intensive mixing of substrate and coupling agent, prefer-ably, however in organic solvents or in aqueous medium.
The concentration of the coupling agent in these procedu-res is in the range from about 0.01 to 20, preferably 0.1 to 10% by weight. Furthermore, it is also possiblQ to use mixtures of coupling agents.

The platelet-like substrates which have been surface-modified in this way have a number of advantages in comparison with untreated sub~trates.

For instance, in humidity and adhe~ion tests, far better results are obtained from pearl lustre pigments which have been treated with silanes such as aminoalkylalkoxy-silanes or 3-glycidyloxypropyl~ilane, than with untreated pigments.

Preferred titanate and zirconate agents are the mono-alkoxy titanates (RR) such as KR TTS, RR 6, RR 7, gR 12, RR 26 S, KR 38 S and RR 44, the so-called quat titanates and quat zirconates such as KR 138 D, XR 158 D, RR 238 T, RR 238 M, XR 238 A, RR 238 J, KR 262 A, LICA 38 J, LZ 38 J, the coordinated titanates and zirconates such as RR 41 B, RR 46 B, RR 55, RZ 55, the neoalko~y titanates such as LICA 01, LICA 09, ~ICA 12, LICA 38, LICA 44, LICA 97, LICA 99 and the neoalkoxy zirconates such as LZ 01, LZ
09, L2 12, LZ 33, LZ 38, L~ 39, LZ 44, LZ 49, LZ 89 and LZ 97.

Some of the pigments treated with quat titanates or zirconates have a very long settling time in water. This is advantageous on i~corporating the pigments in water-borne paints. Some neoalkoxy zirconate-cQated pigments have considerably les~ photoactivity than untreated pigments.

Furthermore, it is also possible to use oxyacetate-chelate titanates, A,B-ethylene-chelate titanates and cycloheteroato-titanates and -zirconates.

Particular preference is given to the quat titanates and quat zirconates, the coordinated titanates and zirconates and the neoalkoxy titanates and zirconates.

Of tho abovementioned compounds, RR TTS, ~R 6, RR 7, RR
41 B and RR 55 ar~ known for coating pigments and other cosmetic material (EP 0,306,056).
The present invention aecordingly al~o provides coatings 21~2~

of platelet-like sub~trates containing all of the other abovementioned coupling agents, in particular the quat titanates and quat zirconates and also coordinated zirconates and neoalkoxy zirconates, owing to the surpri-sing and advantageous properties of the coated sub-strates, for example of the pigments.

In particular, the invention also provides zirconium aluminate-coated platelet-like substrates, for example pigments. With these pigments also, the settling time of the treated pigments in water is significantly greater than that of the untreated pigments. Particularly suit-able coupling agents are the abovementioned ~Cavco Mod~
agents such as Cavco Mod APG, Cavco Mod CPG, Cavco Mod F, Cavco Mod C, Cavco Mod A, Cavco Mod CPM, Cavco ~od C-lP~, Cavco Mod M, Cavco Mod SPM, Cavco Mod APG-2, Cavco Mod MPM, Cavco Mod A PG-l and Cavco Mod APG-3.

The platelet-like substrates which have been coated with the abovementioned coupling agents can be advantageously encapsulated with polymer sy~tems. On the one hand, owing to improved dispersibility, the substrate~ can ba readily incorporated in various polymer systems. On the other hand, stable latex systems can be prepared using pro-cesses such as emulsion polymerization.

The modified platelet-like substrate~ for example a pigment, iB finely di~persed in an aqueou~ ~olution which contains an emulsifier. The emulsifier molecule~ then become prefarentially attached to the hydrophobic pigment particles so that ultimately the hydrophilic functions of the emulsifier molecules are directed into the agueou~
phase. Thi~ gives micelle-like structures which fill up with monomer if the critical micelle concentration is not exceeded or is only ~lightly exceeded. Polymerization then takes place, optionally after adding an initiator, almost exclusively in the pigment micelles. In principle, the amount of monomer to be added can be varied a~
.

2~244~û

required. Owing to the very much greater surface of the micelle~, a radical which has been formed in the aqueous phase much more often encounter~ a micelle filled with monomer molecules than a monomer droplet ~wLmming in the suspension. Monomers which have been consumed in the micelle are renewed from the monomer droplets by dif-fu~ion 80 that even at high monomer concentration polym-erization virtually only occurs in the micelle region.
The amount of monomer can be up to 100% by weight, relative to the ~ubstrate weight, but in individual cases can be considerably more. ~C.H.M. Caris et al., ~Polymeriz~tion at tho surface of inorganic submicron particles", XIX FATIPEX Congress, Aachen 1988). Based on this process principle, all of the polymer reactions which can be carried out in emulsion, for example the polymerization and copolymerization of acrylate, meth-acrylate, styrene, vinyl acetate, butadiene, isoprene, acrylonitrile, vinyl chloride and the like, can be carried out on platelet-like substrates which bear initiator groups. The reaction conditions are Xnown to a person skilled in the art and can, for example, be taken from: D.B. Braun et al.in ~PraXtikum der makromolekularen organischen Chemie~, published by Huthig-Verlag, Heidelberg 1979. The polymer which has been formed on the surface of the pi~ment may be held by physical bonds or be link~d to the pigment surface by a covalent bond to a functional group of the coupling agent for example to a methacrylate group acting as comonomer unit.

;The polymer content of the substrates according to the invention can be controlled for example by the choice of the emulsifier or by the amount of ¦initiator. The polymer content can be determined by product pyrolysis.
Anionic, ca-tionic and nonionic surfactants can be used as emulsifiers.
Emulsifiers which are Nppropriate are for e~ample sodium doclecyl slllphate ~(SDS), sodium oleate, silicon oil (f.e. ME~ nrt. 77~2) and a polyo~yethylene sorbitan monolaurate which is known as tween 20 (ME~ art. 82218~). In individual cases mi~tures of different emulsifiers ar~ acl~alltageous. By after-coating the initial pigments with bnsic aluminillm suLIlhate, an increase of the ~olymer colltellt w~s also observed.

-9a- 2~ 2~

The polymer-encapsulated pigments which have been prepared in this manner can be significantly better incorporated in polymer systems and also have improved weathering resistance. There i~ virtually no los~ of lustre or formation of agglomerates.

Furthermore, it i8 not necessary to isolate the polymer-encapsulated substrate particles.-The substrate/polymer particles formed as pigment latices in the emulsion 2~2~

polymerization can be mixed directly with the compon~nts of a waterborne paint system by latex-intermixing. In this procedure, the polymer coating of the platelet-like substrates can be optimally adapted to the paint system by the appropriate selection of the monomers. The mixing of the harmonized latices allows any incompatibilities and any imperfections in the paint system caused by pigment addition (pigment shock) to be for the greatest part or even completely eliminated.

The invention is explained with the aid of the following examples:

ExamPle 1 Coatings containing coupling agents A) 200 g of Iriodin 504 (iron(III) oxide-coated mica flake pigment from E. Merck, Darmstadt) are suspen-ded in 4 1 of completely deionized water. The reaction suspension is then heated with vigorous stirring to 75C. The pH is ad~usted to 6.5 using 15% aqueous sodium hydroxide solution. Then a solution of 2 g of DYNASYIA~ 1110 in 200 ml of deionized water is added dropwise to the pigment suspension over a period of 10 minutes. During this procedure, the pH is maintained at 6.5 using 5%
aqueous sodium hydroxide solution. After the ad-dition has ceased, the mixture is stirred for a further 30 min at 75C. Then the pigment is filtered off under suction through a suction filter, washed eight times with 2 1 portion~ of deionized water and dried at 100C for 16 h.

Iriodin 225 (TiO2-coated mica flake pigment from E. ~erck, Darmstadt) is similarly coated, but at a pH of 8.

202~ ~ ~ 3 lri()~H~ )225 is simi~nrly~ ~ont-~(l b' it~l D~!;AS~I.A.~IF;MO nt p~l Or 5.5.
Iriodin- 504 i8 similarly coated with DYNASYLAN~
GLYMO at a pH of 7.
In the humidity test (16 h at 66-C in the ~ingle coat humidity test) and in the adhe~ion test (cro~s-hatch adhesion test according to DIN 53 151 using a Du Pont paint system, all of the coated pigments give significantly better result~ than the untreated pigments, by a wide marqin.

B) 61.5 g of LICA 38 J are dissolved in 4500 ml of deionized water and heated to 30-C. Then 1500 g of Iriodin 504 are added in portions to the solution.
After the addition ha~ ceased, the mixture is stirred for a further ~0 min. Then tXe pigment is filtered off, washed three time~ with 4500 ml portions of ~eionized water and dried at 120C for 16 h. It is also possible to use dichloromethane, toluene or isopropanol in the treatment instead of deionized water. However, in this case the opera-tions are carried out at room temperature.
A similar procedure was followed to produce coatings on Iriodin 225 from each of ~R 12, KR 138 1, RR 238 M, KR 238 J, KR 41 B, RR 46 B and LZ 38. The last thr~ abovement~onsd titaniu~ coupling agents are applied dissol~ed in toluene.

The humidity and adhesion test re~ult~ obtained from the coated pigments are comparable with those given under A). The LZ 38-coated pi~ment Iriodin 225 has significantly lower photoactivity (Rronos photo-activity test) than the untreated pigment.

C) 100 g of Iriodin 504 coated with 1% by weight of SiO2 and 1.3% by weight of Al(OH)SO~ are suspended in 2 1 of deionized water. To the reaction suspension which has been ad~usted to a pH of 4 is then added dropwise over a period of 30 min, a solution of ` - 2Q2~

8.47 g of Cavco Mod M 1 (= 2% of acti~e component relative to 100 g of pigment) in 50 ml ~f i~opro-panol. After the dropwise addition has ceased, stirring is continued for a further hour. Then the pigment is filtered off, washed three times with 2 l portions of deionized water and dried for 16 h at 105C.

The Cavco Mod M l-treated pigment can be screened in a third of the time compared with the untreated pigment or commercially available Iriodin 504, the amount screQned in each case being identical.

A similar procedure is followed for treating Iriodin 504 which had been coated with SiO2 and Al(OH)SO~, in accordance with the dirèctions given above, with the zirconium aluminates Cavco Mod APG, Cavco Mod CPG, Cavco Nod F, Cavco Mod C, Cavco Mod A, Cavco Mod CPM, Cavco Mod C-lPM, Cavco Mod M, Cavco Mod 5PM, Cavco Mod APG-2, Cavco Mod MP~, Cavco Mod APG-l and Cavco Mod APG-3. Cavco Mod F and Cavco Mod SPM are added dropwise in the form of isopro-panol solutions, while all of the other zirconium aluminates are added dropwise in the form of aqueous solutions.

The zirconium aluminate-treated pigments ar~ sub-stantially hydrophobic. In aqueous suspension, they are present in particularly finely dispersed form and, in particular, do not form any agglomerates or aggregates. The settling time of the treated pig-ments in water is siqnificantly longer than that of the untreated pigments.

The water used in the examples which follow is in every case completely deionized and thoroughly boiled under an atmosphare of nitrogen.

2~4~

Example 2 40 g of monoalkoxy titanate (KR 12)-coated Iriodin 225 are suspended in 250 ml of water. Then a ~olution of 0.37 g of sodium dodecyl sulphate (SDS) in 186 ml of water is added. The initially hydrophobic pigment par-ticles are now hydrophilic (micelle formation). After adding 62 ml of methyl methacrylate which ha~ been distilled under nitrogen, the mixture is heated to 60C
and stirred vigorously. Then a solution of 1.16 g of potassium peroxodisulphate in 40 ml of water is added.
The viscosity of the solution increases signif$cantly.
Small samples are withdrawn at 10 min intervals and observed under the interference contrast micrascope. No agglomeration of the pigment particles can be observed.
After about one hour, the solution is diluted using 700 ml of water.

This give~ a ~table latex system which can be readily latex-intermixed with various acrylate and methacrylate waterborne paint systems.

A similar procedure is used to obtain latex systems which have good to very good compatibility with the above-mentioned waterborne paint systems, using the pigments Iriodin 504 and Iriodin 225, each modified according to LA, lB ad lC.

Example 3 A procedure similar to that of Example 2 is used to encapsulate 40 g of the Iriodin 504, coated according to Example lB (LICA 38 J), with 40 g of polystyrene.

~efore adding styrene, 50 mg of sodium dihydrogen phos-phate are added to the reaction suspansion, since styrenepolymerizes best in a weakly alkaline medium. The mixture is stirred vigorously for a total of 6 h at 60C. This 2~2~0 gives a stable latex sy~tem which i~ very compatible with other ~tyrene-ba~ed latex sy~tem~.

A sLmilar procedure i~ used to prepare polystyrene-encapsulated modified pigment~ using pigments coated according to lA, lB and lC, and the~e can likewise be well to very well mixed in the form of stable latices with comparable waterborne paint systems.

Example 4 10 g of Iriodin 504, coated according to lC (Cavco Mod M 1), are suspended in 50 ml of water. Then a solution of O.S g of sodium dodecyl sulphate in 2~ ml of water is added followed by 125 mg (0.32 mmol) of iron(II)ammonium sulphate and 125 mg of sodium pyrophosphate in 5 ml of water for buffering purposes. The buffer solution was preheated for about 15 min at 60-70C. The mixture is allowed to cool to room temperature and 20 ml (O.2 mol) of isoprene which has been distilled under nitrogen are added, followed after 15 min o$ vigorous stirring by 50 mg (0.21 mmol) of potassium peroxodisulphate. The mixture is stirred for about 6 h at room temperature.
This give~ a latex system which iY readily compatible with comparable latices.

A s~milar procedure i8 used to prepare likewise readily compatible latex systemY using pigments coated according to LA, lB and lC.
Exam~le 5 30g of Iriodin ~ 225 coated with 1,3Z by weight of Al(OH)SO~ and 2,3% by weight of Dynasyla~ ~1EMO are added at room temperature to a solution of 0.56~ of sns in 260 ml of water. Then the mixture is heated at 60C. Then 3.2 ml of methyl methacrylate are added dropwise followed by a solution of 0.45g of potassium peroxodisulphate in lO ml of water. The mixtl1re is heated at 60C
and stirred for 90 minutes. Then the mixture is allowed to cool to room temperature, the non-reacted monomer is removed in vaclllIm, the product is f;ltered off, w~shed with water and dried At. 120C.

-` -~ 2 Q 2 ~
Tl~ls ~ s a ~m(~ tl~ til~ (tt~ mr!lt ~illl flvery s]o~ pignle~ positioll bella~iollr ill hater, a(et()rle~ ethallol arl(l toluene~
The pol~mer contellt amounts to l.6~% by weight.

EY am~Q 6 A procedure similar to that of example 5 is carried Ollt but only hith 0.09~ of potassium peroxodisulphate. The polymer content amounts to about 0.5X by weight.

Example 7 A procedure similar to that of example 6 is carried out, but 2 ml of silicon oil (MEK art. 7742) are added before adding the monomer. The polymer content amounts to 3.65% by weight.

ExamPIe 8 A procedure similar to that of example 6 is carried out but with 0.93g of sodium oleate as emulsifier. The polymer content amounts to about 1,55 by weight.
Example 9 A procedure similar to that of example 6 is carried out but with 0.56g of the nonionic surfactant tween 20 as emulsifier. The polymer content amounts to about 1.16% by wei~ht.

Exam~le 10 A procedure similar to that of example 5 is carried out but with 0.93g of sodium oleate as emulsifier. The polymer content amounts to about 2.12% by weight.

Claims (5)

1.Polymer-encapsulated platelet-like substrates obtainable by polymerization of an organic monomer system which contains platelet-like substrates which have been surface-modified using organic coupling agents.

2. Latex system containing substrates according to Claim 1.

3. Process for the preparation of latex systems according to Claim 2, characterized in that platelet-like sub-strates are treated with organic coupling agents which are suitable for hydrophobizing the substrate particles, and the substrates which have been modified in this manner are finely distributed in an aqueous solution with the addition of an emulsifier, this giving micelle-like structures, and to this dispersion is added a monomer and optionally an initiator, and the monomer system is polymerized.

4. The use of substrates or latex systems according to at least one of Claims 1 and 2 in formulations such as paints, dye compositions or plastics.

5. Formulations containing substrates or latex systems according to at least one of Claims 1 and 2.