NZ228008A

NZ228008A - Aqueous silicone dispersion and elastomer produced therefrom

Info

Publication number: NZ228008A
Application number: NZ228008A
Authority: NZ
Inventors: Michel Feder; Jean-Pierre Jaubert; Jean Ulrich
Original assignee: Rhone Poulenc Chimie
Priority date: 1988-02-18
Filing date: 1989-02-16
Publication date: 1991-07-26
Also published as: FI890792A0; DE68901286D1; JPH024864A; CA1315451C; AU617422B2; DK73189D0; GR3005147T3; DK73189A; FI890792A; NO890654D0; ZA891205B; CN1035311A; PT89750B; ATE75236T1; NO890654L; FR2627502A1; PT89750A; BR8900807A; KR890013134A; HUT49373A

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number £28008 22 8 00 NO DRAWINGS Priority Date(s): Complete Specification Filed: Class: (5)..fn^rrO. . .Ccs. "L. .feS?J .S. .^v. j.. S .c? !a.US3.. (. qt^. - Publication Date: 2.&.JU4..J99J P.O. Journal, No: — ) J NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION AQUEOUS SILICONE DISPERSION CAPABLE OF CROSSLINKING TO AN ELASTOMER BY ELIMINATING WATER W We, RHONE-POULENC CHIMIE a French Body Corporate of 25 Quai Paul Doumer, 92408 Courbevoie, France hereby declare the invention for which■&/ we pray that a patent may be granted to me/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - (followed by page la) 22 8 008 - 1a- The present invention relates to an aqueous silicone dispersion capable of crosslinking to an elastomer by eliminating water. Patent US-A-2,89 1,920 describes a process for emulsion polymerization of polydiorganosiloxane employing an acidic or ba^c catalyst in the presence of anionic, cat ionic or noniohic surface-active agents. This patent teaches that the emulsions obtained are stable in storage and, after addition of fillers, can be used to produce paints forming a continuous coating by elimination of water. Patent US-A-3,294,725 describes, in particular, the use of dodecyLbenzenesuLphonic acid for polymerizing polydiorganosiloxanes in emulsion. This patent teaches that, in order to obtain stable emulsions, it is desirable to control the pH of these emulsions at a value of approximately 7. This patent teaches that an elastomeric coating can be obtained from these neutralized emulsions, to which colloidal silica and a polyalkoxysilane have been added. The teaching of patent US-A-3,360,491 is similar to that of US-A-3,294,725, except that dodecyLbenzenesuLphonic acid is replaced with Lauryl hydrogen sulphate. Patent US-A-3,355,406 describes, inter alia, a silicone latex comprising: - a colloidal aqueous suspension of an 2 2 8 0 0 a - 2 - a,w-(dihydroxy)polydiorganosiloxane, - a filler necessarily comprising a siIsesquioxane in the form of a colloidal suspension, - a catalyst chosen from inorganic acids, strong 5 bases, dialkyltin diacylates and organic or inorganic peroxides. Patent US-A-3,697,469 describes a particular process for emulsion polymerization of polydiorganosiloxanes and indicates the possibility of adding colloidal silica 10 and a tin salt to this emulsion in order to obtain an elastomeric coating by evaporation of water. French Patent FR-A-2, 11 0 , 358 describes a silicone emulsion with a pH of between 6.5 and 9, crosslinking to an electrically conductive elastomer after evaporation of 15 water by incorporation of carbon black. The emulsion, additionally comprising a tin salt and a polyalkoxysilane, is not stable'tin storage and must be stored in two separate packages (two-component emulsion). US Patents US-A-4,22 1,688 and US-A-4,244,849 and 20 French Patent FR-A-2,463,163 describe silicone emulsions which are stable in storage and comprise: - an anionically stabilized emulsion of an a,u>-(dihydroxy)polydiorganosiloxane polymer, - a siliceous filler, 25 -atinsalt, - if desired, a nonreinforcing filler. The siliceous filler may be a colloidal silica 22 8 0 08 - 3 - (US-A-4,22 1 ,688 ) , sodium silicate (US-A-4,244,849), or an amorphous silica in powder form ( FR-A-2 ,463, 163). When compared with the known aqueous emulsions (dispersions) of the prior art, these three patents teach, 5 on the one hand, that in order to obtain a single-component emulsion which is stable in storage the emulsion must be kept at an alkaline pH higher than 8.5 or 9, preferably higher than 10 and, on the other hand, a tin salt must be incorporated in the emulsion to shorten to a few days the 10 emulsion maturing stage needed to obtain an emulsion which is capable of cross1inking. While the adjustment of the emulsion to an alkaline pH has made it possible to improve the storage stability relative to the known emulsions stored at a 15 neutral or basic pH, it has been found that the elastomer obtained after evaporation of water exhibits a considerable change in its mechanical properties in the course of time, particularly in respect of the elongation, which may be detrimental . 20 This change in mechanical properties is not a phenomenon which surprises a specialist. It is well known, in fact, that silicone polymers depolymerize in an alkaline medium to species of relatively low molecular mass, including monomeric species. 25 These scissions of the silicone chains are, of course, at the source of the changes in the mechanical properties of the elastomer with time, that is to say as - 4 - 2 2 8 0 0 8 it ages. Furthermore, known filled silicone emulsions, stored at an acidic or neutral pH, exhibit at least one of the following disadvantages: 5 - they are not stable in storage when packaged in a single package (single-component composition), - they take an excessively long time to cure to an elastomer, - they are not thixotropic, 10 - they adhere only very weakly to the usual substrates. In what follows, the percentages and parts are on a weight basis, unless stated otherwise. An objective of the present invention is to pro-15 pose an aqueous silicone dispersion capable of crosslink-ing to an elastomer by elimination of water, at ambient temperature, which does not exhibit the disadvantages of the known emulsions, or does so in a highly attenuated form. Another objective of the present invention is to 20 propose a silicone dispersion of the above type, which is stable in storage and which crosslinks correctly and sufficiently quickly to an elastomer by elimination of water at ambient temperature, the elastomer formed retaining its mechanical properties as it ages. 25 Another objective of the present invention is to propose a silicon dispersion of the above type, whose maturing stage can be carried out at a slightly raised 22 8 0 - 5 - temperature (20-60°C) and for a period of less than 48 hours. Another objective of the present invention is to propose a silicone dispersion of the above type, leading to 5 an elastomer additionally exhibiting an improved flame resistance. Another objective of the present invention is to propose a silicone dispersion of the above type, leading to an elastomer exhibiting a satisfactory adhesion to various 10 substrates, particularly to glass, concrete and metals (steel, aluminium). These objectives and others are achieved by the present invention, which provides an aqueous silicone dispersion comprising: 15 (A) - 100 parts of an oil-in-water emulsion of an a,o)-(dihydroxy )polydiorganosiloxane stabilized with at least one anionic or nonionic surface-active agent or a mixture thereof, (B) - 0.1 to 15 parts, calculated on a solids 20 content basis, of an alkali metal or alkaline-earth metal organo-silconate in aqueous solution, (C) - 5 to 250 parts of a nonsiliceous inorganic filler, and (D) - 0.01 to 3 parts of a catalytic compound 25 containing tin, 22 8 0 - 6 - the said dispersion having a pH higher than 8.5, preferably between 19 and 12, and a solids content of at least 40%. The a,<»>-(dihydroxy)polydiorganosiloxanes must have 5 a viscosity of at least 100 mPa s at 25°C, preferably of at least 50,000 mPa s. It is, in fact, at viscosities above 50,000 mPa s that an elastomer is obtained exhibiting a combination of appropriate mechanical properties, particularly in respect of Shore A hardness and of 10 elongation. Furthermore, the higher the viscosity, the more the mechanical properties are maintained as the elastomer ages. The preferred viscosities in the case of the present invention are between 50,000 and 1,500,000 mPa s at 25°C. The organic radicals of the a,a>-(dihydroxy)poly-15 diorganosiloxanes are monovalent hydrocarbon radicals containing up to 6 carbon atoms, optionally substituted by cyano or fluoro groups. The substituents which are generally employed because of their availability in industrial products are methyl, ethyl, propyl, phenyl, vinyl 20 and 3,3,3-trifluoropropyl radicals. At least 80% of the number of these radicals are generally methyl radicals. Within the scope of the present invention it is more especially preferable to employ the a,o>-(dihydroxy)- 22 8 0 Of - 7 - polydiorganosiloxanes prepared by the anionic polymerization process described in the abovementioned US Patents: US-A-2,891,920 and above all, US-A-3,294,725 (which are mentioned as a reference). The polymer obtained is stabil-5 ized anionically with a surface-active agent which, in accordance with the teaching of US-A-3,294,72 5, is preferably an alkali metal salt of an aromatic hydrocarbon sulphonic acid, the free acid also acting as a polymerization catalyst. 10 The preferred surface-active agents are dodecyLbenzenesuLphonic acid and its alkali metal salts, especially its sodium salt. If desired, other anionic or nonionic surface-active agents may be added. However, this addition is not necessary because, in accordance 15 with the teaching of US-A-3,294,725, the quantity of anionic surface-active agent resulting from the neutralization of the sulphonic acid is sufficient to stabilize the polymer emulsion. This quantity is generally less than 3 % , preferably 1.5 % of the weight of the emulsion. 20 This emulsion polymerization process is particu larly advantageous because it makes it possible to obtain the emulsion (A) directly. Furthermore, this process enables a,w-(dihydroxy)poI ydiorganosiI oxane emulsions (A) of very high viscosity to be potentially obtained 25 without difficulty. To prepare the emulsion (A) it is also possible to start with an already polymerized a, to— < d i hydroxy ) - 22 8 008 P ■ poLydiorganosiloxane, and then to convert it into an aqueous emulsion by stabilizing the emulsions with an anionic and/or nonionic surface-active agent according to a process which is well known to the specialist and des- 5 cribed in detail in the literature (see, for example, g | S"~6 I 3 0I £> O § 1 33^ 19 *§"" ;Patents F-ft- 'A-2,064,5 63, r R A 2,094,31211, F R - A-2 , 1 1 4 , 230 ;irl and EP-A-1 69, 098 ) . ;(fc>/ ;According to this process, the a,oj-( d i h y d r 0 x y ) po I y-di0rganosiI 0xane polymers are mixed simply by stirring 10 with the anionic or nonionic surface-active agent, it being possible for the latter to be in aqueous solution, then water is added if necessary and the whole is converted into a fine and homogeneous emulsion by passing through a conventional colloid mill. ;15 The millbase obtained is subsequently diluted with a suitable quantity of water and an emulsion (A) stabilized with an anionic or nonionic surface-.active agent and stable in storage is thus obtained. ;The quantity of anionic and nonionic surface-20 active agent which can be employed is that commonly employed for making use of the emu Isification process, particularly those described in the abovementioned patents and in patent US-A-2,891,920. ;Within the scope of the present invention, the 25 preferred anionic surface-active agents are the alkali metal salt of an aromatic hydrocarbon sulphonic acid and the preferred nonionic surface-active agents are ;- 9 - ;22 S O 08 ;po I yoxyethyLenated alkyLphenoLs. These nonionic surface-active agents are obviously the same as those which may be added, if desired, to the emulsions (A) obtained by emulsion polymerization as indicated above. ;5 The emulsion (A) prepared by emulsion polymeriza tion or by emulsifying the silicone polymer is in the form of an oil-in-water emulsion and preferably has a dry solids content of more than 45 % by weight. ;From 0.1 to 15, preferably from 0.5 to 5, parts, 10 calculated on a solids content basis, of an alkali metal or alkaline-earth metal organosiIicon ate in aqueous solution are incorporated per 100 parts of emulsion (A). ;These alkali metal or alkaline-earth metal organo-siliconates are known products most of which are available 15 commercially. The most common ones are sodium or potassium methylsiliconates with a solids content of approximately 30 to 60 %. ;The alkali metal organosiIiconates may be prepared, for example, by hydrolysis of the corresponding organo-20 silanes containing 3 hydrolysable groups such as halogen atoms or alkoxy radicals, followed by dissolving of the product obtained in a solution of a strong inorganic base, in such proportions that there is at least one equivalent of base per silicon atom (see, for example, US-A-2,441,422, 25 US-A-2,441,423 and US-A-2,507,200 ). ;Another constituent of the dispersion according to the invention is the addition of. 5 to 250, preferably ;- 10 - ;22 8 0 0 8 ;of 10 to 200, parts of a semireinforcing or packing inorganic filler (C). ;The fillers (C) have a particle size which is generally between 0.001 and 300 urn and a BET surface 5 area of less than 100 m^/g. ;Examples of the fillers (C) which can be used by themselves or mixed are carbon black, titanium dioxide, aluminium oxide, hydrated alumina, expanded vermiculite, unexpanded vermiculite, calcium carbonate, zinc oxide, 10 mica, talc, iron oxide, barium sulphate and slaked lime. ;These fillers (C) are introduced into the emulsion in the form of dry powder, for example simply by mixing. ;According to an alternative form of the invention, 15 it has been found that if the filler (C) consists substantially only of a filler chosen from hydrated alumina, expanded vermiculite and unexpanded vermiculite in a proportion of 5 to 250, preferably of 50 to 200, parts per 100 parts of emulsion (A), an elastomer is obtained which 20 has a particularly high flame resistance which cannot be obtained with the other categories of filler (C) which are mentioned above, particularly with aluminium oxide or unhydrated alumina. Ceramic or aramide fibres may also be incorporated according to the teaching of EP-A-212,827. 25 The constituent (0) is a catalytic tin compound, ;generally an organotin salt, preferably introduced in the form of an aqueous emulsion. The organotin salts which ;F, ;- 11 - ;22 8 0 0 8 ;can be used are described particularly in the work by Noll, Chemistry and Technology of Silicones, Academic Press (1968), page 337. ;The reaction product of a tin salt, particularly 5 of a tin dicarboxylate with ethyl polysilicate, as described in patent US-A-3,862 , 9 1 9, may also be employed as a catalytic tin compound. ;It is also possible to employ the reaction product of an alkyl silicate or of an alkyltrialkoxysilane with 10 dibutyltin diacetate, as described in Be I g i an Patent <-+• lo3- Sr-fao. ;frfc-A^fl42,305". ;The preferred tin salts are tin bischelates (EP-A-147,323 and EP-A-235,049 ) , diorganotin dicarboxy I ates and, in particular, dibutyl- or dioctyltin diversatates (British 15 Patent GB-A-1,289,900), dibutyl- or dioctyltin diacetate, ;and dibutyl- or dioctyltin dilaurate. From 0.01 to 3, preferably from 0.05 to 2, parts of organotin salt are employed per 100 parts of (A). ;According to an alternative form, a siliceous 20 additive (E) chosen from sodium silicate (0.3 to 30 parts) and a reinforcing or semireinforcing siliceous filler (1 to 150 parts) may also be incorporated, per 100 parts of emulsion (A ). ;These siliceous fillers are chosen from colloidal 25 silica or pyrogenic and precipitated silica powders or a mixture thereof. Pyrogenic silica is preferred. However, semireinforcing siliceous fillers such as diatomaceous ;- 12 - ;22 8 0 0 9 ;earths and ground quartz may also be employed. ;The sum of the parts of (C) + (E) must be less than 300 parts per 100 parts of emulsion (A). ;These silica powders are well known; they are 5 employed particularly as fillers in silicone elastomer compositions which can be vulcanized to a silicone rubber by heating. These powders have a mean particle size which is generally below 0.1 ym and a BET specific surface area ;2 2 ;higher than 50 m / g , preferably between 150 and 350 m /g. ;10 The incorporation of this siliceous additive (E) ;in the emulsion (A) by any suitable means, particularly by stirring, greatly increases the viscosity of the emulsion (A) which then appears pasty in nature. ;It has been found, in fact, in accordance with the 15 present invention that the addition of this siliceous additive (E) is sufficient to impart a more or less marked thixotropic character to the dispersion. The dispersion, for example when extracted from a storage cartridge, adheres even to a vertical substrate without running and 20 cures to an elastomer by evaporation of water at ambient temperature. An emulsion which does not flow can also be obtained by using as filler (C) calcium carbonate whose mean particle diameter is less than 0.1 pm. Obviously, slight heating (to approximately 40-80°C) of the compos i-25 tion to accelerate the evaporation of water is not excluded from the scope of the invention. ;Various additives enabling the properties of ;- 13 - ;22 8 0 08 ;dispersions and of the elastomers formed from the dispersions by elimination of water to be modified may be added, if desired, to the dispersions in accordance with the present invention. ;5 It is possible, in particular, to incorporate an additive (F) chosen from organotriaLkoxysilanes such as, for example, vinyltrimethoxysilane, alkyl silicates such as methyl silicate or ethyl silicate or a product of their partial hydrolysis, that is to say a IkyLpoIysi I i-10 cates such as methyl polysilicate and ethyl polysilicate in a proportion of 0.1 to 20 parts of additive (F) per 100 parts of emulsions (A). The additive (F) allows the cohesion of the elastomeric material obtained after elimination of water to be improved. 15 The organotriaLkoxysilanes and the alkyl silicates preferably correspond to the general formula: ;R'aSi(0R)4_a in which R is an alkyl radical containing from 1 to 4 carbon atoms, R' is R or vinyl and a is 1 or 0. ;20 Other examples of additives which may be mentioned are fungicides and foam suppressors, as well as thixo-troping agents such as carboxymethyl cellulose, xanthan gum and polyvinyl alcohol. ;The dispersions according to the invention may 25 be employed for producing silicone elastomer seals, particularly for building. ;These dispersions can also be employed for ;- 14 - ;22 8 0 0 8 ;coating various pharmaceutical or plant-protection active substances formulated in a solid form (pellets, tablets, pills, and the like), for coating cork stoppers employed for closing wine and spirit bottles, for producing coat-5 ings of kitchen articles and, as a general rule, of articles in contact with foodstuffs (for example bread yeasts - ;Known coating techniques can be employed, particularly brush and dip (immersion) coating methods, 10 spraying techniques, fluidized bed coating techniques and immersion coating techniques may be employed. ;In the case of the coatings for cork stoppers, a recommended technique is the dipping method, which consists in immersing the stoppers in the dispersion, which 15 wets the surface of the stopper, and then evaporating off water. ;The coating obtained represents 20 to 50 mg of elastomer per 100 c m ^ of stopper surface. This layer makes it easier for the stopper to slide in the neck of 20 the bottle during the bottling and then prevents "running", that is to say leakages of liquid between the neck and the stopper. ;The dispersions according to the invention may be prepared in the following manner: 25 The starting point is an emulsion (A) prepared either by the emulsion polymerization process, in whicn case as emulsion stabilized by an anionic and, if desired, ;22 8 0 0 8 ;nonionic surface-active agent is available, or by the process of emulsifying the a,w-(dihydroxy)poIydiorgano-si loxane in which case an emulsion stabilized with an anionic and/or nonionic surface-active agent is available. 5 0.1 to 15 parts of organosiIiconate (B) are mixed first of all with 100 parts of this emulsion (A), followed by 0.01 to 3 parts of the catalytic tin compound (D) and finally 5 to 250 parts of filler (C). ;The siliceous additive (E) and the additive (F) 10 are added, if desired, to this mixture. ;A dispersion which directly exhibits a pH higher than 8.5 is generally obtained. When this is not the case or when it is desired to raise the pH, the pH is adjusted by adding an inorganic or organic acid or base. 15 Primary amines such as diethylamine may be em ployed as an organic base. However, according to a preferred embodiment of the invention, the pH is adjusted to the desired value by means of an appropriate quantity of an inorganic base introduced in the form of an aqueous 20 solution preferably chosen from solutions of alkali metal and alkaline-earth metal hydroxides such as sodium hydroxide, potassium hydroxide, and solutions of calcium hydroxide, barium hydroxide and magnesium hydroxide. However, alkali metal and alkaline-earth metal hydroxides 25 may be introduced directly in a solid form. ;The constituents (A), (B), (C), (D) and, if desired, (E) and (F) are mixed in such quantities that ;22 8 0 0 8 ;- 16 - ;the final dispersion has a solids content of more than 40 %, preferably more than 60 %, but generally below 90 %. The preferred pH range is between 9 and 12. ;The dispersions according to the invention may 5 be employed as a paint capable of crosslinking as a thin layer. They then preferably have a solids content of between 40 and 70 %. ;To determine the solids content, 2 g of dispersion are placed in an aluminium weighing dish and this 10 is heated for one hour to 150°C in an oven with air circulation. After cooling the dish is reweighed and the residual material is determined as a percentage of the initial 2 g, representing the solids content. ;According to a preferred alternative form, after 15 being prepared, the dispersion according to the invention undergoes a maturing stage preferably at a pH above 8.5, optionally by being heated to a temperature of 20°C and 60°C for a period which is generally at least one hour and generally shorter than 72 hours. 20 The higher the maturing temperature, the shorter can be the maturing time. ;This maturing stage makes it possible to obtain, after elimination of water, an elastomer which immediately has appropriate mechanical properties. ;25 In what follows and what precedes, the percent ages and parts are on a weight basis, unless stated otherwise. ;22 8 0 0 8 ;- 17 - ;- EXAMPLE 1: ;An emulsion (A) of a,w-(dihydroxy)polydimethyl-siloxane oil is prepared by emulsion polymerization in the presence of free dodecylbenzenesulphonic acid and of 5 its sodium salt. ;The oil present in the emulsion has a viscosity of 10^ mPa s at 25°C. The emulsion (A) obtained contains 1.5 parts of sodium salt of dodecyLbenzenesuLphonic acid (DBSNa) per 100 parts of emulsion, and has a solids con-10 tent of 58%. ;7 parts of potassium methyls iliconate with a solids content of AO % are first of all added to 173 parts of emulsion (A), followed by 2.6 parts of a tin-based emulsion containing 40 % by weight of dioctyltin 15 dilaurate (D), and are homogenized at 25°C. ;After 10 minutes' homogenization, 150 parts of CaC03 with a mean particle size of 5 ym are added. ;The final dispersion has a solids content of 70 % and has directly a pH above 9. ;20 This runny dispersion is subjected to a maturing at 25°C for 48 hours. ;Films (surface layers) are prepared by spreading the dispersion, after maturing if desired, on a flat surface and water is allowed to evaporate at ambient 25 temper ature. ;The following average mechanical properties are measured on the films dried for 7 days at ambient ;22 8 0 Off ;- 18 - ;temperature : ;- the Shore A hardness (SAH) according to ASTM standard D 2240, ;- the tensile strength (T/S) according to AFNOR 5 standard T 46 002 corresponding to ASTM standard 0 412, ;i n MP a s, ;- the elongation at break (EB) in % according to AFNOR standard T 46 002, ;- the elasticity modulus (EM) at 100% elongation 10 according to AFNOR standard T 46 002. ;The composition of the dispersion and the mechanical properties obtained are collated in Table 1 below. ;The elastomer obtained exhibits good adhesion to glass, concrete and aluminium. ;15 To evaluate the adhesion, a strand of aqueous dis persion 4 mm thick is deposited onto a glass or concrete substrate. After 12 days, the adhesion of the elastomer formed is evaluated by pulling the strand manually. The adhesion is good on both substrates, since the strand 20 cannot be unstuck from its substrate by hand. ;- EXAMPLE 2 : ;The operating procedure of Example 1 is followed precisely, except that: ;- the surfactant employed is a 50/50 weight ;25 mixture of dodecyLbenzenesuLphonic acid (DBSA) and a 70/ 30 weight mixture of polyoxyethylenated 2-nonylphenols, one containing 10 OCH2CH2 units and the other 20 OCH2CH2 ;- 19 - ;22 8 0 0 8 ;units (NPP), ;- the viscosity of the oil is 85,000 mPa s, and the solids content of the emulsion (A) is 58%, ;- calcium carbonate is replaced with hydrated 5 alumina with a mean particle size of 100 ym. ;The dispersion obtained is runny. ;The composition of the dispersion and the mechanical properties obtained are collated in Table 1 below. ;10 The elastomer obtained exhibits good adhesion to glass, concrete and aluminium and a remarkable self-extinguishing character. ;- EXAMPLE 3 : ;The operating procedure of Example 1 is followed 15 precisely, except that: ;- the viscosity of the oil is 85,000 mPa s and the solids content of the emulsion (A) is 58%, ;- the 150 parts of calcium carbonate with a mean particle size of 5 um are replaced with 150 parts of ;20 calcium carbonate with a mean particle size of 0.08 urn. ;The dispersion obtained does not flow. ;The composition of the dispersion and the mechanical properties obtained are collated in Table 1 below. ;The elastomer obtained exhibits good adhesion 25 to glass, concrete and aluminium. ;The EB, SAH and EM are measured on three other batches of dried films, after natural aging for 5 months ;22 8 0 0 8 ;at ambient temperature (20°C), after accelerated aging in a ventilated oven for 7 days at 50°C and after accelerated aging for 42 days at 50°C, respectively. ;The results obtained are collated in Table 2 ;5 below. ;- EXAMPLE 4 : ;The operating procedure of Example 1 is followed exactly, except that: ;- the tin catalyst employed is the product of 10 reaction of one mole of dioctyltin oxide with one mole ;D ;of versatic acid with elimination of the water formed. The reaction product is emulsified. This emulsion contains 8.55% by weight of tin metal, ;- the 150 parts of calcium carbonate with a mean 15 particle size of 5 um are replaced with 150 parts of calcium carbonate with a mean particle size of 0.08 um. ;The dispersion obtained does not run. The composition of the dispersion and the mechanical properties obtained are collated in Table 1 below. 20 The elastomer obtained exhibits good adhesion to glass, concrete and aluminium. ;The SAH, TS and EB are measured on a batch of dried films after aging for 28 days at 50°C. ;The values found are: SAH : 25, TS : 0.97 MPa 25 and EB : 428%. ;- EXAMPLE 5 : ;The operating procedure of Example 1 is followed ;- 21 - ;22 8 0 0 $ ;exactly, except that: ;- the silicone oil of the emulsion (A) has a viscosity of 10^ mPa s at 25°C and a solids content of 58.6%, ;5 - the 150 parts of calcium carbonate with a mean particle size of 5 ym are replaced with 100 parts of calcium carbonate with a mean particle size of 0.08 um. ;The dispersion obtained does not run. ;The composition of the dispersion and the 10 mechanical properties obtained are collated in Table 1 below. ;The elastomer obtained exhibits good adhesion to glass, concrete and aluminium. ;The SAH, TS and EB are measured on a batch of 15 dried films after natural aging for 8 months at ambient temperature (20°C). ;The values found are : SAH : 16, TS : 0.88 MPa and EB : 428%. ;22 3 0 0 8 ;- 22 - ;TABLE 1 ;EXAMPLE S ;1 ;2 ;3 ;4 ;5 ;Emulsion CA) ;173 ;173 ;1 73 ;173 ;173 ;o> ;Siliconate (B) ;7 ;7 ;7 ;7 ;7 ;<D 3 ;Tin emulsion (D) ;2.6 ;2.6 ;2.6 ;2.6 ;2.6 ;>> X) ;Calcium carbonate (5 pm) ;150 ;- ;- ;- ;- ;CO 4-* L. Calcium carbonate (0.08um) - - 150 1 50 100 (tJ a. Hydrated alumina - 1 50 - - - pH of the emu L s i on > 9 > 9 > 9 > 9 > 9 Maturing at 25°C (in hours) 48 48 48 48 48 SAH 8 18 22 20 27 TS (MPa s) 0.36 0.29 1 .50 1 .33 2.57 i EB i I (%) 1 160 80 I 91 5 910 1 257 </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 22 8 0 0 8 - 23 - TABLE 2 EB (%) SAH ' ! EM (MPa) After 7 days at 20°C 91 5 22 0.35 After 7 months at 20°C 670 1 9 0.20 After 7 days at 50°C 680 20 0.25 After 42 days at 50°C 420 1 8 0.19 22 8 0 0 8 - 24 - WHAT WE CLAIM IS:

1. Aqueous silicone dispersion which comprises by weight: (A) - 100 parts by weight of an oil-in-water emulsion of an a,w-(dihydroxy)polydiorganosiloxane 5 stabilized with at least one anionic or nonionic surface-active agent or a mixture thereof, (B) - 0.1 to 15 parts by weight, calculated on a solids content basis, of an alkali metal or alkaline-earth metal organosiliconate in aqueous solution 10 (C) - 5 to 250 parts by weight of a nonsiliceous inorganic filler, and (D) - 0.01 to 3 parts by weight of a catalytic tin compound, the said dispersion having a pH higher than 8.5 and 15 a solids content of at least 40%.

2. Silicone dispersion according to Claim 1, in which the tin salt (D) is in the form of an aqueous emulsion.

3. Silicone dispersion according to Claim 1 or 20 2, in which the emulsion (A) has a solids content of at least 45% by weight.

4. Silicone dispersion according to any one of the preceding claims, in which the filler (C) is hydrated alumina, alumina, calcium carbonate, expanded vermiculite, 22 8 0 - 25 - unexpanded vermiculite, carbon black, zinc oxide, titanium dioxide, mica, talc, iron oxide, barium sulphate or slaked lime.

5. Silicone dispersion according to Claim 4, in 5 which the filler (C) is calcium carbonate with a mean particle diameter of less than 0.1 //m.

6. Silicone dispersion according to any one of the preceding claims, which comprises: (A) : 100 parts of an oil-in-water emulsion of an 10 a,o>-(dihydroxy)polydiorganosiloxane with a viscosity at 25°C of between 50,000 and 1,500,000 mPa s, stablilized with an alkali metal salt of an aromatic hydrocarbon sulphonic acid or a polyoxyethylenated alkylphenol, (B) : 0.5 to 5 parts of an organosiliconate, 15 (C) : 50 to 200 parts of an inorganic filler, and (D) : 0.05 parts to 2 parts of a diorganotin dicarboxylate, the said dispersion having a pH of between 9 to 12 and a solids content of at least 60%. 20

7. Silicone dispersion according to any one of the preceding claims, which additionally comprises, per 100 parts of an emulsion (A), a siliceous additive (E) chosen from sodium silicate (0.3 to 30 parts), and a reinforcing or semireinforcing siliceous filler (1 to 150 parts), provided 25 that the sum of the parts of (C) + (E) is less than 300 parts per 100 parts of (A). ? 2800.8 - 26 -

8. Silicone dispersion according to any one of the preceding claims, which additionally comprises, per 100 parts of emulsion (A), from 0.01 to 20 parts by weight of an additive (F) chosen from organotrialkoxysilanes, alkyl 5 silicates and alkyl polysilicates.

9. Process for the preparation of a silicone dispersion as defined in any one of claims 1 to 8, which comprises: 1) - mixing the emulsion (A) and the 10 organosiliconate (B), 2) - adding the nonsiliceous filler (C) and the catalyst (D), 3) - adjusting the pH if necessary to a value of more than 8.5; the total quantity of water employed being 15 such that the solids content of the final dispersion obtained is at least 40%.

10. Process according to Claim 9 in which a siliceous filler additive (E) as defined in claim 7 or additive (F) as defined in claim 8 is added in step 2). 20

11. Process according to claim 9 or 10, in which the dispersion obtained is subjected to a maturing stage at a temperature of between 20 and 60°C for a period of at least one hour, before being packaged in the absence of air.

12. Elastomer obtained by curing by evaporation of 25 water from a dispersion as defined in any one of claims 1 to 8.

13. Use of an aqueous dispersion as defined in^^Tf^: one of claims 1 to 8 for coating and encapsulating I ^ ^ Ay fc»( ; •' » f • .'S; / i O •C o u I) o - 27 - pharmaceutical or plant-protection active substances and for producing coatings of articles in contact with foodstuffs. 5

14. Use according to Claim 13, in which the said articles in contact with foodstuffs are cork stoppers for packaging wines and spirits.

15. Silicone dispersion according to Claim 1, substantially as described in any one of Examples 1 to 5. 10

16. Process for the preparation of a silicone dispersion according to Claim 9, substantially as described in any one of Examples 1 to 5.

17. A silicone dispersion when prepared in accordance with the process as claimed in any one of claims 15 9 to 11 and 16. By WeZMor/Their Authorised Agents, A. J. PARK & SON </div>