AU730772B2

AU730772B2 - Aqueous dispersion based on silicones and on organic (co) polymer latex, for the preparation of a silicone elastomer with adjustable translucency

Info

Publication number: AU730772B2
Application number: AU63095/96A
Authority: AU
Inventors: Michel Feder; Mathieu Joanicot; Alain Morin; Roland Reeb; Jean-Francois D'allest
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1995-05-19
Filing date: 1996-06-12
Publication date: 2001-03-15
Anticipated expiration: 2016-06-12
Also published as: WO1997047687A1; ES2140871T3; EP0904321A1; DE69606333D1; IL127431A0; FR2734273B1; AU6309596A; CA2258148A1; EP0904321B1; ATE188983T1; HUP9904098A3; RU2162866C2; DE69606333T2; JPH11513060A; PL330598A1; DK0904321T3; HUP9904098A2; FR2734273A1; CZ402498A3

Abstract

The invention discloses a silicon and organic (co)polymer latex based aqueous dispersion, cross-linking by eliminating water through drying in ambient conditions into an elastomer with adjustable translucency having high mechanical properties, characterised in that it is not provided with any reinforcing mineral filler and in that it comprises the following constituents: (A) an oil-in-water emulsion with 100 parts by weight of an oil or a polymer alpha , omega -(dihydroxy)polydiorganosiloxane (A1) and 1 to 100 parts by weight of an organosilicic cross-linking agent (A2), the said emulsion being stabilised by at least one surfactant (A3) selected among anionic and non-ionic surfactants and their mixtures; and with a particle size between 0.1 mu m (100 nm) and 100 mu m (100000 nm); and having a dry extract content of at least 60 wt.%; (B) for 100 parts by weight of oil or polymer (A1), 1 to 100 parts by weight of an aqueous dispersion of at least an organic (co)polymer with a particle size of 0.01 mu m (10 nm) to 10 mu m (10000 nm), and a dry extract of 10 to 70 wt.%; (C) optionally, for 100 parts by weight of oil or polymer (A1), 0.01 to 5 parts by weight of a hardening catalytic metal compound. The dispersions are useful in producing translucid silicon elastomers for the building industry.

Description

WO 97/47687 1 PCT/FR96/ 00891 AQUEOUS -DISPERSION BASED ON SILICONES AND ON ORGANIC (CO) POLYMER LATEX, FOR THE PREPARATION OF A SILICONE ELASTOMER WITH ADJUSTABLE

TRANSLUCENCY

The present invention relates to an aqueous dispersion based on silicone compounds and on an organic (co)polymer latex, which can crosslink, into an elastomer with adjustable translucency, by elimination of water through drying under ambient conditions. The invention also relates to the process for obtaining it and to its use in the building industry in the preparation of silicone elastomer products with adjustable translucency such as, in particular, sealing and weatherproofing mastics, protective coatings and skins for facades.

Aqueous dispersions based on silicones which can crosslink into a translucent elastomer for use in the preparation of products for the building industry have already been described in the prior art. Thus, in US-A-4,824, 89 0, the basic aqueous dispersion is a mixture of a silicone microemulsion with a particle size of less than 0.15 Am (150 nm), prepared by emulsion polymerization of a cyclopolydiorganosiloxane, with (2i) 5 to 30 parts by weight (per 100 parts of the silicone polymer) of colloidal silica and (3i) 1 to parts by weight (per 100 parts of the silicone polymer) of a dialkyltin dicarboxylate catalyst; in EP-A-0,542, 498 the basic aqueous dispersion is a mixture of an aqueous emulsion of a crosslinked silicone polymer, which is the product of crosslinking of a silicone oil containing silanol ends with an alkoxysilane in the presence of a tin-based catalyst, having less than 10% of particles with a particle size of greater than 1 Am (1000 nm) with (2i) 0.7 to 2 parts by weight (per 100 parts by weight of the crosslinked silicone polymer) of a specific surfactant consisting of an ammonium or alkali metal alkyl sulphate, and with, for the purpose of leading to an elastomeric product having mechanical properties which make it useful in the building industry, (3i) 2.5 to 45 parts by weight (per 100 parts by weight of the silicone polymer) of colloidal silica used in the form of an aqueous dispersion with a particle size of less than 0.06 im (60 nm).

These aqueous dispersions which can crosslink into a translucent elastomer nevertheless have drawbacks, among which mention may be made of: insufficient stability on storage; this is because the system has a tendency to give rise to a gel on account of the premature occurrence of condensation reactions which can take place between the silicone polymer and the colloidal silica, which is reactive via its surface hydroxyl groups; a level of translucency which is mainly adjustable only by adjusting the content of the silicic -3feedstock; now, it is known that any variation in the silica content is liable to substantially modify some of the essential properties of the elastomer, in particular the mechanical breaking properties, the elasticity and the adhesion; adjusting the elastomer's translucency therefore cannot be done without at the same time modifying other essential properties.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

9

S

4* 21553-OO.DOC For the purposes of the present invention, the expression "adjustable translucency" means that the level of translucency can readily be adjusted in order to cover the entire range extending from total opacity to a high translucency close to transparency.

The mechanical properties concerned in the present specification are the properties which are essential for the elastomer product to be capable of ensuring its function of lining joints, irrespective of the climatic conditions; mention will be made in particular of: the secant modulus at 100% elongation, the elongation at break, the breaking strength, the elasticity and the adhesion.

15 The use of a combination of silicone(s) and of an organic latex is already taught in EP-A-0,410,899 for increasing the solids content, while at the same time retaining a suitable viscosity, of aqueous silicone dispersions of the type in which a reinforcing inorganic filler is present in order to be able to obtain, by elimination of water, elastomeric products, which are moreover opaque, with high mechanical properties.

None of the documents contained in the prior art teaches the use, in accordance with the subject of the present invention, of a polymeric feedstock in order to obtain elastomeric products with adjustable translucency for the building industry, while at the same time maintaining good mechanical properties without using a reinforcing inorganic filler.

According to a first aspect, the invention provides an aqueous dispersion based on silicones and on organic (co)polymer(s) which crosslink, by elimination of water through drying under ambient conditions, into an elastomer with adjustable translucency which has high mechanical properties, free of any reinforcing inorganic filler and comprising the following constituents: an oil-in-water emulsion based on 100 parts by weight of an oil or of an ca, co- (dihydroxy) poly-diorganosiloxane polymer having a viscosity of at least 100 mPa.s 10 at 25 0 C (Al) and on 1 to 100 parts by weight of an organosilicon crosslinking agent the said emulsion: being stabilized by at least one surfactant (A3) chosen from anionic and nonionic surfactants and mixtures thereof, having a particle size of between 0.1 um (100 nm) and 100 pm (100,000 nm), 15 having a solids content of at least 60% by weight; per 100 parts by weight of oil or polymer from 1 to 100 parts by weight of an aqueous dispersion of at least one organic (co)polymer having: a particle size of between 0.01 pm (10 nm) and 10 pm (10,000 nm); a solids content of between 10 and 70% by weight; the said polymer particles being derived from a process of emulsion (co)polymerization of organic monomer(s), said polymerizable monomers consisting of at least one main monomer chosen from styrene butadiene acrylic esters and vinyl nitriles 21553-OO.DOC -6optionally, per 100 parts by weight of oil or polymer from 0.01 to 5 parts by weight of a catalytic metallic curing compound chosen from carboxylic acid salts, halides of metal chosen from lead, zinc, zirconium, titanium, iron, tin, barium, calcium and manganese; organotin salts including tin bischelates and diorganotin dicarboxylates; and the reaction product of an alkylsilicate or of an aryltrialkoxysilane with dibutyltin diacetate; the said aqueous dispersion having a solids content of at least 60% by weight; the translucency of the elastomeric product to be formed being adjusted, during the 10 preparation of the aqueous dispersion, by adjusting to the desired value(s): either the size of the polymer particles in the latex or the refractive index of the polymer constituting the latex by modifying the chemical composition of the organic (co)polymer; or the two above mentioned parameters, size and refractive index, at the S**same time.

4 15 a solids content of between 10 and 70% by weight; optionally, per 100 parts by weight of oil or polymer from 0.01 to 5 parts by weight of a catalytic metallic curing compound; the said aqueous dispersion having a solids content of at least 60% by weight; the translucency of the elastomeric product to be formed being adjusted, during the preparation of the aqueous dispersion, by adjusting to the desired value(s): either the size of the polymer particles in the latex or the refractive index of the polymer constituting the latex by modifying the chemical composition of the organic 21553-00.DOC 6a (co)polymer; or the two abovementioned parameters, size and refractive index, at the same time.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

The final aqueous dispersion is prepared by simple intimate mixing of all of its constituents, leading to a homogeneous dispersion which is stable on storage in the absence of air.

10 Those skilled in the art know that the scattering power of a particle [in this instance, the polymer particles in the latex in a continuous medium [in this instance, 0 the silicone matrix obtained after crosslinking phase by elimination of water], which controls the opacity of the elastomer (inversely proportional to its translucency), decreases with: 0 15 the particle size, and 0 05@0 21553-00.DOC 7 the difference in refractive indices between the particle and the continuous medium.

This teaching is in accordance with the Rayleigh scattering law, which allows the scattering power Pd of a particle to be expressed by the equation: where x 27r/X with r average radius of the particle and X wavelength of the light, and m nl/n2 with nl refractive index of the particle and n2 refractive index of the continuous medium.

EMULSION Oil or polymer (Al): The a,w-(dihydroxy)polydiorganosiloxanes must have a viscosity of at least 100 mPa.s at preferably at least 50,000 mPa.s.

The reason for this is that it is for viscosities of greater than 50,000 mPa.s that an elastomer with a set of suitable mechanical properties is obtained, in particular as regards the elongation at break and the breaking strength.

In addition, the higher the viscosity, the more the mechanical properties are conserved during ageing of the elastomer.

The preferred viscosities for the present invention are between 50,000 and 1,500,000 mPa.s at 25 0

C.

The viscosity referred to here is the dynamic viscosity at 25 0 C; it is measured using a Brookfield viscometer according to the indications of AFNOR standard NFT 76102 of May 1982.

The organic radicals of the a,w-(dihydroxy)polydiorganosiloxanes are monovalent hydrocarbon-based radicals containing up to 6 carbon atoms, optionally substituted with cyano or fluoro groups. The substituents generally used on account of their availability in industrial products are methyl, ethyl, propyl, phenyl, vinyl and 3,3,3-trifluoropropyl radicals. In general, at least 80%, in numerical terms, of these radicals are methyl radicals.

Crosslinkinq agent (A2): As indicated above, a crosslinking agent of organosilicon nature is used. The list of crosslinking agents recommended will be found below, with, for each of them, the precise amounts recommended in the emulsion which take account of the nature of the crosslinking agent used, these amounts being expressed in parts by weight per 100 parts of oil or polymer (Al): 1 to 15 parts of an organosiliconate; 1 to 100 parts of a silsesquioxane resin microemulsion according to the combined teaching of US-A-3,355,406 and US-A-3,433,780; to 100 parts of a reactive silicone resin of low molecular mass containing alkoxy and acyloxy groups; to 100 parts of a toluene-insoluble silicone resin of high molecular mass; 5 to 100 parts of a hydroxysilicone resin containing, per molecule, at least 2 different units chosen from those of formulae: R 3 SiO0.

5

R

2 SiO RSiO 1 s

(T)

and SiO 2 R mainly being a C 1

-C

6 alkyl, vinyl or 3, 3 ,3-trifluoropropyl radical, and having a hydroxyl group weight content of between 0.1 and 10%. Among these resins, introduced just as they are or in the form of aqueous emulsions, mention may be made of the resins MQ, MDQ, TD and MTD; 1 to 20 parts of a silane of formula: RaSiX4a in which R is a monovalent organic radical, in particular methyl or vinyl, a is 1 or 0, X is a condensable and/or hydrolysable group preferably chosen from alkoxy, acyloxy, ketiminoxy, alkylamino, amido and alkenyloxy groups and the various possible mixtures thereof. When X is an alkoxy, it is desirable to add 2-amino-2-methylpropanol as stabilizer, in accordance with the teaching of EP-A-0,259,734.

The crosslinking agent (A2) which is used is referably included in the 5 to 100 parts of the hydroxysilicone resin which has just been mentioned.

Surfactant (A3): In the context of the present invention, the surfactants used include anionic surfactants which can be chosen, for example, from the alkylbenzene sulphonates, the alkyl sulphates, the alkyl ether sulphates, the alkylaryl ether sulphates and the dioctyl sulphosuccinates of alkali metals, and mixtures thereof. The preferred anionic surfactants are the polybenzene sulphonates of alkali metals.

The surfactants used can also be nonionic; as examples, mention may be made.of alkoxylated fatty acids, polyalkoxylated alkylphenols, polyalkoxylated fatty alcohols, polyalkoxylated or polyglycerolated fatty amides, polyglycerolated a-diols and alcohols, ethylene oxide/propylene oxide block polymers, polydiorganosiloxanes containing siloxyl units bearing ethylene oxide chains or propylene oxide chains as well as alkyl glucosides, alkyl polyglucosides, sucroethers, sucroesters, sucroglycerides, sorbitan esters, ethoxylated compounds of these sugar derivatives and mixtures of these surfactants. The preferred nonionic surfactants are polyalkoxylated alkylphenols and polyalkoxylated fatty alcohols.

As an embodiment which is also preferred, a mixture of preferred nonionic surfactant(s) with one (or more) preferred anionic surfacant(s) can be used.

The surfactants, taken alone or as a mixture, are chosen as a function of the nature of the silicone oil or polymer (Al) to be emulsified; an HLB of about 11 to 15 is generally chosen to emulsify an oil or polymer (Al) consisting of an a,w- (dihydroxy)polydiorganosiloxane.

Preparation of the emulsion A: To prepare the emulsion A, an emulsion polymerization process which gives the emulsion (A) directly can be used. Moreover, this process allows emulsions comprising an a,w-(dihydroxy)polydiorganosiloxane of very high viscosity to be obtained without difficulty.

According to this process, the oil-in-water emulsion of the silicone phase is prepared by the technique of anionic polymerization of an oil (Al) with a low viscosity ranging from 100 mPa.s to 1000 mPa.s, this polymerization optionally being carried out in the presence of the crosslinking agent which, according to another procedure, can also be added later, after the polymerization. Such an anionic polymerization process is described in American patents US-A-2,891,920 and especially US-A-3,294,725 (cited as reference). The polymer obtained is anionically stabilized by a surfactant which, in accordance with the teaching of US-A-3,294,725, is preferably the alkali metal salt of a sulphonic aromatic hydrocarbonbased acid, the free acid also acting as a =a polymerization catalyst.

12 The preferred catalyst and surfactant are dodecylbenzenesulphonic acid and its alkali metal salts, in particular its sodium salt. Other anionic or nonionic surfactants can optionally be added. However, this addition is not necessary since, in accordance with the teaching of US-A-3,294,725, the amount of anionic surfactant resulting from the neutralization of the sulphonic acid is sufficient to stabilize the polymer emulsion. This amount is generally less than preferably 1.5% of the weight of the emulsion However, in accordance with the present invention, it is preferred to start with a prepolymerized ct, w- (dihydroxy) polydiorganosiloxane and then to place it in aqueous emulsion, in the presence of the crosslinking agent while stabilizing the emulsions with an anionic and/or nonionic surfactant according to a process which is well known to those skilled in the art and described in detail in the literature (see for example patents FR-A-2,064,563, FR-A-2,094,322, FR-A-2,114,230 and EP-A-0,169,098) According to this process, the a,w- (dihydroxy)polydiorganosiloxane polymers (Al) are mixed, by simple stirring, with the crosslinking agent (A2) and with the anionic and/or nonionic surfactant it being possible for this surfactant to be in aqueous solution, water is then added, if necessary, and the mixture is converted into a fine, homogeneous emulsion by passing it through a standard colloid mill.

The ground material thus obtained can optionally be diluted with a suitable additional amount of water. An emulsion stabilized by an anionic or nonionic surfactant, which is stable on storage, is thus obtained.

The emulsion prepared by emulsion polymerization or by placing the silicone polymer (Al) in emulsion is in the form of an oil-in-water emulsion with a solids content of greater than or equal to by weight and preferably between 80 and 98% by weight.

It should be noted that a very viscous silicone polymer (Al) with a viscosity of greater than 30,000 mPa.s can advantageously be emulsified by applying the process described in document WO-A-94/09058 (cited as reference), which is characterized by very precise control over the value of the ratio of the respective viscosities of the aqueous phase, on the one hand, and of the silicone phase, on the other hand.

It would not constitute a departure from the context of the present invention to prepare all or part of the emulsion by the emulsion polymerization technique or by the preferred technique of emulsification, this polymerization or this emulsification being carried out directly in the presence of the latex starting with all or some of the constituents (Al) and (A2).

DISPERSION OF LATEX Latex The latex is formed of an aqueous suspension of polymer particles derived from a process of emulsion (co)polymerization of polymerizable organic monomer(s).

The main polymerizable monomers consist of at least one main monomer chosen from styrene butadiene acrylic esters and vinyl nitriles The term acrylic esters denotes esters of acrylic acid and of methacrylic acid with CI-C, 2 alkanols, preferably Cl-C, alkanols, such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and isobutyl methacrylate.

The vinyl nitriles include those containing from 3 to 12 carbon atoms, in particular acrylonitrile and methacrylonitrile.

The styrene can be partially or totally replaced with a-methylstyrene or vinyltoluene.

In addition to the abovementioned main monomers to it is possible to copolymerize some of these main monomers with up to 40% by weight, relative to the total weight of the monomers, of at least one other ethylenically unsaturated monomer or compound chosen from: vinyl esters of a carboxylic acid, such as vinyl acetate, vinyl versatate or vinyl propionate; ethylenically unsaturated mono- and dicarboxylic acids, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid; monoalkyl esters of the dicarboxylic acids mentioned above in with alkanols containing from 1 to 4 carbon atoms, and the N-substituted derivatives thereof; unsaturated carboxylic acid amides, such as acrylamide, methacrylamide, N-methalolacrylamide or -methacrylamide; ethylenic monomers containing a sulphonic acid group and its ammonium or alkali metal salts, for example vinlysulphonic acid, vinylbenzenesulphonic acid, a-acrylamidomethylpropanesulphonic acid or 2-sulphoethylene methacrylate; ethylenically unsaturated monomers containing a secondary, tertiary or quaternary amino group or a heterocyclic group containing nitrogen, for example vinylpyridines, vinylimidazole, aminoalkyl(meth)acrylates and aminoalkyl(meth)acrylamides, such as dimethylaminoethyl acrylate or methacrylate, Sdi-tert-butylaminoethyl acrylate or 16 methacrylate, dimethylaminomethylacrylamide or -methacrylamide, as well as zwitterionic monomers, such as sulphopropyl(dimethyl)aminopropyl acrylate; esters of (meth)acrylic acids with alkanediols preferably containing 2-8 carbon atoms, such as glycol mono(meth)acrylate, hydroxypropyl mono(meth)acrylate or 1,4-butanediol mono(meth)acrylate, as well as monomers containing two polymerizable double bonds, such as ethylene glycol dimethacrylate.

In addition to the monomers to (k) mentioned, it is also possible to use, in smaller amounts, of between 0.1 and 5% by weight relative to the total weight of the monomers, unsaturated ethylenic monomers of crosslinkable nature, such as glycidyl (meth)acrylate or vinyl and acrylic silanes such as vinyltrimethoxysilane and vinyltriethoxysilane.

In addition to the abovementioned monomers to it is also possible to use, in amounts ranging up to 40% by weight relative to the total weight of the ethylenically unsaturated monomers or compounds, a functionalized polyorganosiloxane (n) bearing at least one ethylenically unsaturated function (for example a vinyl or (meth)acrylic function), which can react, via a radical route, with at least one of the ethylenically unsaturated monomers to plus, optionally, at least one of the monomers to 17 and optionally at least one other reactive function (for example an epoxyfunctional or hydroxyfunctional group) (cf. in particular EP-A-0,635,526).

As dispersion which can be used in the context of the present invention, mention will be made in particular of those containing homopolymers derived from the monomers and As copolymer latices mention will be made in particular of latices containing copolymers derived from: at least one and at least at least one at least two at least one at least one and at least at least one at least one monomer at least one monomer (d) one monomer monomer and at least one monomer monomers of different nature; monomer and at least one monomer monomer at least one monomer (e) one monomer monomer and at least one monomer monomer and at least one monomer In accordance with the Rayleigh scattering law mentioned earlier, it is observed, for a given silicone matrix, that the translucency of an elastomer containing a polymeric feedstock, in this instance the polymer particles of the latex with a particle size of between, for example, 0.01 Am (10 nm) and 0.06 Am nm), is always greater than that of an elastomer containing the same polymeric feedstock but in this case having a substantially larger particle size, i.e.

greater than 0.06 Am (60 nm). It is also observed that for a given size (small or large) of the particles in the polymeric feedstock, the translucency is always greatly improved by reducing the refractive index of the feedstock polymer, i.e. by appropriately modifying the chemical composition of the said polymer.

In accordance with a preferred embodiment of the invention, giving an elastomer with translucency which is adjustable within a zone of medium to high values, a latex is used having: a particle size of between 0.01 Am (10 nm) and 0.08 Am (80 nm), and preferably of between 0.02 Am nm) and 0.06 Am (60 nm), and a solids content of between 10 and 50% by weight.

In accordance with a more preferred embodiment, which achieves the above-intended translucency objective, a latex is used which has the small particle size and the solids content indicated above and which contains the following acrylic (co)polymers: acrylic homopolymers obtained from a monomer and copolymers obtained, partly or totally, either from acrylic monomers or from at least one monomer and at least another acrylic monomer taken from the group formed by the monomers taken as (meth)acrylic acids, the monomers taken as acrylic derivatives, and the monomers In the case of copolymers derived partly from acrylic monomers or and/or and/or an amount of acrylic monomers of between 70% and 99% by weight relative to the total weight of the monomers, and preferably between 80% and 99% by weight relative to the total weight of the monomers, is used.

Needless to say, the mechanical properties of the latices depend to a large extent on the monomers chosen to prepare them. The polymers constituting the latices can have a glass transition temperature Tg of between -70 0 C and +230 0

C.

In accordance with an even more preferable embodiment of the invention, the aqueous dispersions which are used are the latices defined above in the context of the so-called "more preferable" embodiment, in which the constituent acrylic polymers have a glass transition temperature Tg of between +500C and +130 0

C.

The choice of these Tg values makes it possible to obtain the maximum reinforcing efficacy (better values for the breaking properties).

The polymers constituting the latices (B) have a refractive index n which is generally between 1.34 and 1.60. This index is calculated by the simplified Gladstone-Dale equation: in which xi and n i represent the voluminal fraction and the refractive index of each constituent of the polymer (cf. the book Polymer Handbook, 1989, pages VI/452 to VI/461).

In accordance with a most especially preferred embodiment of the present invention, the aqueous dispersions which are used are the latices defined above in the context of the so-called "even more preferable" embodiment, for which the index n of the polymers is between 1.34 and 1.50.

In accordance with a different embodiment of the invention, giving an elastomer with translucency which is adjustable within a zone of values substantially less than the zone of medium to high values mentioned earlier with regard to the preferred embodiments of the invention, a latex is used: which has a particle size between a value just greater than 0.08 pm (80 nm) and 10 Am, and preferably between a value just greater than 0.08 Am (80 nm) and 2 Am; and a solids content of between 30% and 70% by weight; and which contains the acrylic (co)polymers defined above in the context of the so-called "more ,2 preferable" embodiment.

21 In accordance with a different and preferred embodiment of the invention, the aqueous dispersions which are used are the latices defined above in the context of the so-called "different" embodiment, in which the constituent acrylic polymers have a glass transition temperature Tg of between +50 0 C and +130 0

C.

In accordance with a different and more preferable embodiment, the aqueous dispersions (B) which are used are the latices defined above in the context of the so-called "different and preferred" embodiment, for which the index n of the polymers is between 1.34 and 1.50.

Preparation of the latex A person skilled in the art knows how to prepare the latices There are several ways of preparing aqueous dispersions of organic polymers; the dispersions can be obtained: by radical polymerization in emulsion; by direct polymerization of a microemulsion of the corresponding monomer(s); by emulsification and evaporation of solvent: this process consists in dissolving the polymer in a water-immiscible solvent which has a boiling point below that of water, then emulsifying the polymer solution in water and then removing the solvent by evaporation; by precipitation in a non-solvent: this process consists in dissolving the polymer in a watermiscible solvent and then in precipitating the polymer from water; by coacervation: this process consists, starting with a homogeneous solution, in obtaining phasedemixing with formation of a colloidal phase (rich in polymer) by modifying physical factors such as the pH or the temperature.

The process which is preferably used for the preparation of the latices which fall within the context of the present invention is the process by radical polymerization in emulsion.

As regards the latices with a small particle size of between 0.01 Am (10 nm) and 0.08 Am nm), which are used in the context of the preferred embodiments of the invention, they are prepared by a more preferred radical polymerization process, described in EP-A-0,644,205 (cited as reference), which involves the incremental introduction of monomer(s) into an aqueous reaction medium with introduction, also optionally incremental, of free-radical initiator(s).

THE METALLIC CURING COMPOUND The compound in particular for certain cross-linking agents (A2) such as siliconate, is optional, but, in the context of the present invention, it is recommended to use The catalytic metallic curing compounds (C) are essentially the carboxylic acid salts and the halides of metals chosen from lead, zinc, zirconium, titanium, iron, tin, barium, calcium and manganese.

The constituent is preferably a catalytic tin compound, generally an organotin salt, preferably introduced in the form of an aqueous emulsion. The organotin salts which can be used are described in particular in the book by Noll, Chemistry and Technology of Silicones Academic Press (1968), page 337. Such an emulsion can be stabilized, if necessary, for example with polyvinyl alcohol.

The reaction product of an alkyl silicate or of an aryltrialkoxysilane with dibutyltin diacetate can also be used, as described in Belgian patent BE-A-842,305.

The preferred tin salts are tin bischelates (EP-A-0,147,323 and EP-A-0,235,049), diorganotin dicarboxylates, and in particular dibutyltin or dioctyltin diversatates (British patent GB-A-1,289,900), dibutyltin or dioctyltin diacetate, and dibutyltin or dioctyltin dilaurate. From 0.01 to 3, preferably from 0.05 to 2, parts of metallic curing compound are used per 100 parts of (Al).

OTHER OPTIONAL ADDITIVES: The aqueous dispersions according to the invention can also comprise one or more additive(s), such as, in particular: optionally, per 100 parts by weight of oil or polymer from 0.1 to parts by weight of an adhesion agent; 24 optionally, per 100 parts by weight of oil or polymer from 0.1 to 5 parts by weight of a nonionic, anionic or cationic organosilicon surfactant; optionally, an effective amount of at least one compound taken from the group formed by antifungal agents, antifoaming agents, antifreezes such as ethylene glycol and propylene glycol, and thixotropic agents such as carboxymethylcellulose and xanthan gum.

Preferably, the adhesion agent is chosen from organosilicon compounds bearing both organic groups substituted with radicals chosen from the group of amino, ureido, isocyanato, epoxy, alkyenyl, isocyanurate, hydantoyl and mercapto ester radicals and hydrolysable groups linked to the silicon atoms.

For illustrative purposes, mention may be made of the organosilicon compounds corresponding to the formulae below (accompanied by the numbers of the patents in which they are described): O NH CH,- Si(CH) -N EP-A-0 074 001

H

2 N CH 2 CMl-MN-CH- CH(CH,) -COO(CH;- Si(OCH, DE-A-3 304 182 [(CH3)3C- 2sI(ocoOIA US-A-4 356 116 CH COO(CHA)Si(OCH4, I I CMi .COO(CH 2 )lSi(OCOCH,) 3 US-A-4 273 698 N H-CO I 3

C(CH,)

2

-CO

EP-A-0 031 996 (CHO)Si(Ct 2 3 NHCO CH C -COOH 466 739 (OH6O),Si(CH )30CHj-CH-

CH,

0 US-A-4 115 356 (CAHO),Si(CH)NH CH- CO I CN-C4 CH4 FR-A-2 269 833 Preferably, the organosilicon surfactant (E) is chosen from polyorganosiloxanes functionalized either with ethylene oxide or propylene oxide chains (an agent of this type is commercially available under the trade name Tegopren, type 30, 58 or 70, from the company Goldschmidt), or with salified amino groups (an agent of this type is also commercially available under the trade name Tegopren, type 69, from the company Goldschmidt), or with metal sulphonate groups (cf. in this respect, the book: Surface Phenomena and Additives in Water-Based Coatings and Printing Technology; edited by M.K. Sharma, Plenum Press, New-York, 1991, pages 73 to 82, which describes agents of this type).

PREPARATION OF THE AQUEOUS DISPERSION OF THE INVENTION To prepare the aqueous dispersions according to the invention, it is recommended that the dispersion is first added to the emulsion with stirring at room temperature, followed by the metallic curing catalyst optionally in the form of an aqueous dispersion or emulsion, and optionally the additive(s) 27 and/or It is recalled that it is possible partly or totally to carry out the emulsion polymerization or the emulsification of the emulsion in the presence of the dispersion The pH of the aqueous dispersion can be acidic, neutral or basic. However, it is recommended to adjust the pH of the dispersion to a value of greater than 7, preferably between 8 and 13, using a strong organic base or, preferably, a strong inorganic base (triethanolamine, and preferably sodium hydroxide and potassium hydroxide).

The final dispersion obtained is homogenized, then degassed and is then packaged in a wrapping which is leaktight to atmospheric oxygen and to water vapour.

The constituents and optionally and/or are mixed in amounts such that the final emulsion has a solids content at least equal to by weight, preferably between 80 and 95% by weight.

In order to determine the solids content, 2 g of dispersion are placed in an aluminium weighing crucible, which is heated for 3 hours at 50 0 C in an oven with circulation of dry air. After cooling, the crucible is reweighed and the percentage of material remaining out of the initial 2 g is determined, which represents the solids content.

According to a preferred variant, after the dispersion according to the invention has been prepared, it undergoes a maturation step, at room 28 temperature, of from a few hours to a few days.

This maturation step consists simply in leaving the dispersion to stand in the absence of atmospheric oxygen before it is used.

The dispersions according to the invention can be used in the building industry for the preparation of translucent silicone elastomer products, in particular sealing and weatherproofing mastics and water-repellent coatings for building surfaces or skins for facades in contact' with bad weather, at a dose, for example, of from 20 to 100 g of dispersion per m 2 of surface to be treated.

The examples which follow illustrate the invention without limiting its scope.

EXAMPLE 1 (for comparison) An emulsion is prepared by introducing, into a 5-litre Meili mixer with beating arms: 1000 g of an a,w-(dihydroxy)polydimethylsiloxane oil with a viscosity of 80,000 mPa.s at 60 g of a hydroxysilicone resin introduced just as it is, containing 0.5% by weight of hydroxyl groups, consisting of 62% by weight of CH 3 SiO 1 units and 24% by weight of (CH 3 2 SiO units and 14% by weight of (CH 3 3 SiO 0 5 units; this resin is soluble in toluene and has a molecular mass of about 1000 and a CH 3 /Si molar ratio of 45 g of Genapol X080, sold by the company Hoechst, which is a nonionic surfactant, i.e. a 29 polyalkoxylated (with about 8 ethylene oxide units) fatty alcohol (containing 13 carbon atoms); and 35 g of water.

The final mixture obtained is homogenized for 180 minutes.

The emulsion A thus obtained has an average particle size of 0.5 Am (500 nm) and a solids content of 96.9% by weight.

The ingredients below are incorporated into the emulsion in the same mixer, with stirring for minutes for each additive: an aqueous dispersion of precipitation CaCO 3 with a solids content of 43.6%, consisting of: 280 g of precipitation CaCO 3 with an average particle size of 0.07 pm (70 nm), i.e. a volume equivalent to that of the particles in the polymeric feedstock of the following examples, 13 g of dispersant in the form of an aqueous solution containing 40% by weight of sodium polyacrylate and 323 g of water; 10 g of aqueous emulsion containing 38% by weight of di-n-octyltin dilaurate stabilized with 5% by weight of polyvinyl alcohol relative to the tin salt; and 0 22 g of aqueous potassium hydroxide solution with a solids content of The final dispersion has a pH of 12 and a solids content of 81.3% by weight.

After storing for 4 days, samples are prepared which will be used to measure the various desired properties mentioned below: Mechanical properties of breaking and elasticity: The dispersion is spread out with a scraper paddle onto a Teflon plate in order to make films mm in thickness, which are left to dry for 7 days in an air-conditioned room (temperature 23 0 C 2 0

C;

relative humidity: 55% The following properties are measured on test pieces H2 cut from the dried film: the elongation at break (EB, as a and the breaking strength (BS, in MPa) according to the indications of AFNOR standard T-46002, the elasticity as a of the mastic by a relaxation test under the following conditions: 100% elongation of the sample at a speed of 300 mm/min, followed by relaxation of the elongated sample for 15 minutes. The elasticity, as a is evaluated by the formula 100(1-Cls/Co) where C O and C 15 are the constraints suffered by the sample on stopping the elongation (Co) and minutes later (C 15 The elasticity is evaluated on the average of 3 test samples.

Translucency: A flat-bottomed crucible 4 mm in depth is filled with the dispersion and this assembly is dried for 10 days in an air-conditioned room (temperature: 31 23°C 2 0 C; relative humidity: 55% The translucency of the sample is determined by its contrast ratio (CR, as a on black and white backgrounds. This ratio is measured with the Datacolor machine sold by the company of the same name, under the following lighting conditions: diffuse lighting, luminance C 10 with anti-UV and anti-glare filters. The translucency is evaluated by the contrast ratio CR Y black background/Y white background x 100 i.e.

CR/100 is the ratio of the Y (green light) of the trichromic coordinates of the light reflected at 90 0

C

by the elastomer sample, placed on black and white backgrounds respectively.

Adhesion: The adhesion in newtons) of the elastomer is estimated by a T peeling test, at an angle of 1800, on a clear glass support, at a speed of 50 mm/min, of a film of mastic 25 mm in width, after drying for 7 days at 23 0 C 2 0 C and 55% 5% relative humidity.

The film of mastic is reinforced with a nylon-66 large-mesh polyamide fabric in the following way: a first film 1.5 mm in thickness is deposited, onto which the polyamide strip is unwound; a second layer of aqueous silicone dispersion is deposited on the assembly using a 2.5 mm scraper paddle, which leads to a mastic-polyamide-mastic sandwich structure.

All the properties measured are collated in Table II below.

32 EXAMPLES 2 to 7 (according to the invention): The process is performed as indicated above in Example 1, except that the aqueous CaCO 3 dispersion is now replaced with 330 g of a latex of fine particle size.

Characteristics of the nanolatices used: TABLE I Example Composition Solids Average Tg n by weight) content size in (OC) MMA STY BuA MAA VTEO by wt.) nm (3) 2 90 0 0 10 0 30 40 114 1.493 3 35 0 55 10 0 30 40 1 1.480 4 0 0 90 10 0 30 40 -42 1.472 100 0 0 0 0 30 40 105 1.489 6 95 0 0 0 5 30 40 105 1.489 MMA methyl methacrylate; STY styrene; BuA butyl acrylate; MAA methacrylic acid; VTEO vinyltriethoxylsilane.

Tg is measured by differential scanning calorimetry (or DSC) analysis, according to the indications of AFNOR standard T 51-5077.

Refractive index n of the (co)polymer: this is calculated from the indices for the homopolymers according to the Gladstone-Dale additivation rule: 33 n polystyrene 1.591, n polyacrylic acid 1.527, n polymethyl methacrylate 1.485, n polybutyl acrylate 1.4666.

General procedure for preparing the nanolatices: 3 g of sodium lauryl sulphate, 240.3 g of water and 0.5 g of an aqueous solution containing by weight of ammonium persulphate are successively introduced into a 1-litre stainless steel reactor fitted with a stirrer and a water-circulation jacket for regulating the temperature inside the reactor. The reactor contents are then brought to a temperature of and 100 g of the mixture of ethylenically unsaturated monomers are then introduced continuously, over a period of 2 hours. The dispersion is then cooled and filtered.

A blue-grey latex with a solids content of by weight and an average particle size of 0.04 pm nm) is obtained.

The final dispersions, of Examples 2 to 7, obtained, have a pH of 12 and a solids content of 81.3%.

The properties of the elastomers reinforced with the nanolatices, as well as those of the reference elastomer with carbonate, are collated in Table II below: 34 TABLE II CR EB BS E A (MPa) (N) Example 1 (for comparison) 100 935 0.75 26.5 0.1 Example 2 93.0 930 0.89 29.2 Example 3 88.6 675 0.50 21.3 0.1 Example 4 76.3 640 0.33 26.8 0.1 Example 5 87.9 935 0.51 30.6 Example 6 90.0 730 0.77 42.9 Compared with an elastomer reinforced with carbonate, the elastomers reinforced with the nanolatices have comparable, if not better, mechanical properties and are markedly more translucent.

Claims

1. Aqueous dispersion based on silicones and on organic (co)polymer(s) which crosslink, by elimination of water through drying under ambient conditions, into an elastomer with adjustable translucency which has high mechanical properties, free of any reinforcing inorganic filler and comprising the following constituents: an oil-in-water emulsion based on 100 parts by weight of an oil or of an a, CO- (dihydroxy) poly-diorganosiloxane polymer having a viscosity of at least 100 mPa.s at 25 0 C (Al) and on 1 to 100 parts by weight of an organosilicon crosslinking agent the said emulsion: .il 10 being stabilized by at least one surfactant (A3) chosen from anionic and nonionic surfactants and mixtures thereof, having a particle size of between 0.1 im (100 nm) and 100 upm (100,000 nm), having a solids content of at least 60% by weight; per 100 parts by weight of oil or polymer from 1 to 100 parts by weight of an aqueous dispersion of at least one organic (co)polymer having: a particle size of between 0.01 pm (10 nm) and 10 p.m (10,000 nm); a solids content of between 10 and 70% by weight; the said polymer particles being derived from a process of emulsion (co)polymerization of organic monomer(s), said polymerizable monomers consisting of at least one main monomer chosen from styrene butadiene acrylic esters and vinyl nitriles optionally, per 100 parts by weight of oil or polymer from 0.01 to 5 parts by weight of a catalytic metallic curing compound chosen from carboxylic acid salts,

21553-00.DOC -36- halides of metal chosen from lead, zinc, zirconium, titanium, iron, tin, barium, calcium and manganese; organotin salts including tin bischelates and diorganotin dicarboxylates; and the reaction product of an alkylsilicate or of an aryltrialkoxysilane with dibutyltin diacetate; the said aqueous dispersion having a solids content of at least 60% by weight; the translucency of the elastomeric product to be formed being adjusted, during the preparation of the aqueous dispersion, by adjusting to the desired value(s): either the size of the polymer particles in the latex or the refractive index of the polymer constituting the latex by modifying the chemical composition of the organic 10 (co)polymer; or the two above mentioned parameters, size and refractive index, at the •same time.

2. Dispersion according to claim 1, wherein the ca, co-(dihydroxy)polydiorgano- siloxanes (Al) must have a viscosity of at least 50,000 mPa.s at 25 0 C and in that the organic radicals of these siloxanes are monovalent hydrocarbon-based radicals 15 containing up to 6 carbon atoms, optionally substituted with cyano or fluoro groups.

3. Dispersion according to claim 1 or 2, wherein the crosslinking agent (A2) is chosen from: an organosiliconate; a silsesquioxane resin microemulsion resin; a reactive silicone resin of low molecular mass containing alkoxy and acyloxy groups; a toluene-insoluble silicone resin of high molecular mass; 21553-00DOC -37- a hydroxysilicone resin containing, per molecule, at least 2 different units chosen from those of formulae: R 3 SiO 0 5 R 2 SiO RSiO 1 .5 and SiO 2 R mainly being a CI-C 6 alkyl, vinyl or 3,3,3-trifluoropropyl radical, and having a hydroxyl group weight content of between 0.1 and a silane of formula: RaSiX 4 -a in which R is a monovalent organic radical, in particular methyl or vinyl, a is 1 or 0, X is a condensable and/or hydrolyzable group preferably chosen from alkoxy, acyloxy, ketiminoxy, alkylamino, amido and alkenyloxy groups and the various possible mixtures thereof.

4. Dispersion according to any one of claims 1 to 3, wherein the aqueous dispersion 10 is the one containing organic (co)polymers which are derived: from the (co)polymerization of at least one main monomer chosen from styrene butadiene acrylic esters and vinyl nitriles it being possible for some of these main monomers to to be copolymerized with up to 40% by weight, relative to the total weight of the monomers, of at least one other monomer or 15 unsaturated compound chosen from the group formed by: vinyl esters of a carboxylic acid; ethylenic unsaturated mono- and dicarboxylic acids; monoalkyl esters of the dicarboxylic acids mentioned above in with alkanols containing from 1 to 4 carbon atoms, and the N-substituted derivatives thereof; unsaturated carboxylic acid amides; ethylenic monomers containing a sulphonic acid group and its ammonium or AQ alkali metal salts; ethylenically unsaturated monomers containing a secondary, tertiary or 21553-OO.DOC -38- quaternary amino group or a heterocyclic group containing nitrogen, as well as zwitterionic monomers; esters of (meth)acrylic acids with alkane-diols preferably containing 2-8 carbon atoms, as well as monomers containing two polymerizable double bonds; glycidyl methacrylate; vinyl or acrylic silanes; a functionalized polyorganosiloxane bearing at least one ethylenically unsaturated function which can react, via a radical route, with another ethylenically unsaturated monomer. 10

5. Dispersion according to any one of claims 1 to 4, wherein, with the aim of producing an elastomer with translucency which is adjustable within a zone of medium to high values, a latex is used having: a particle size of between 0.01 [m (10 nm) and 0.08 gm (80 nm), and a solids content of between 10 and 50% by weight. 15

6. Dispersion according to claim 5, wherein: the aqueous dispersion or latex is that containing: acrylic homopolymers obtained from a monomer and copolymers obtained, partly or totally, either from acrylic monomers or from at least one monomer and at least another acrylic monomer taken from the group formed by the monomers taken as (meth)acrylic acids, the monomers taken as acrylic derivatives, and the monomers and 21553-00.DOC -39- in the case of copolymers derived partly from acrylic monomers or (f) and/or and/or an amount of acrylic monomers of between 70% and 99% by weight relative to the total weight of the monomers is used.

7. Dispersion according to claim 6, wherein the aqueous dispersion is that containing acrylic organic (co)polymers with a glass transition temperature Tg of between +50°C and +130°C.

8. Dispersion according to claim 7, wherein the aqueous dispersion is that containing acrylic organic (co)polymers with a Tg of between +50°C and +130°C, for which the refractive index f is between 1.34 and 1.50. 10

9. Aqueous dispersion according to any one of claims 1 to 3, wherein, with the aim of producing an elastomer with translucency which is adjustable within a zone of values less than the zone of medium to high values mentioned earlier in claim 5, a latex is used: S- which has a particle size between a value just greater than 0.08 um (80 nm) and tm; and a solids content of between 30% and 70% by weight; and S: which contains the acrylic (co)polymers defined above in claim 6. Aqueous dispersion according to claim 9, wherein the aqueous dispersion is that containing acrylic organic (co)polymers with a glass transition temperature Tg of between +50°C and +130°C. 11. Aqueous dispersion according to claim 10, wherein the aqueous dispersion is that containing acrylic organic (co)polymers with a Tg of between +50°C and +130°C, for which the refractive index i is between 1.34 and 1.50. 21553-00.DOC 12. Aqueous dispersion according to any one of claims 5 to 8, wherein the latex B has a particle size of between 0.02 pm (20 nm) and 0.06 4m (60 nm). 13. Aqueous dispersion according to any one of claims 9 to 11, wherein the latex B has a particle size between a value just greater than 0.08 pm (80 nm) and 2 gm. 14. Aqueous dispersion according to any one of claims 1 to 13, wherein: the emulsion has a solids content of from 80 to 98% by weight; the final aqueous dispersion has a solids content of from 80 to 95% by weight. Aqueous dispersion according to any one of claims 1 to 14, wherein the metallic compound is an organotin salt in the form of an aqueous emulsion.

10 16. Process for the preparation of an aqueous dispersion as defined in claims 1 to wherein the dispersion is first added to the emulsion at room temperature, followed by the metallic curing catalyst optionally in the form of an aqueous dispersion or emulsion, and the optional additive(s). 17. Process according to claim 16, wherein the pH of the final aqueous dispersion is 15 adjusted to a value of greater than 7 by adding a strong inorganic base. 18. Use of an aqueous dispersion as defined in any one of claims 1 to 16, in the building industry in the preparation of translucent silicone elastomeric products consisting of sealing and weatherproofing mastics, protective coatings and skins for facades. 19. An aqueous dispersion substantially as herein described with reference to any one of the examples, but excluding any comparative examples. 21553-00.DOC -41- A process for the preparation of an aqueous dispersion substantially as herein described with reference to any one of the examples, but excluding any comparative examples. 21. The use of an aqueous dispersion substantially as herein described with reference to any one of the examples, but excluding any comparative examples. DATED this 15th Day of January 2001 RHODIA CHIMIE Attorney: CHARLES W. TANSEY Registered Patent Attorney of 10 The Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS 21553-00DOC