NO872597L - ORGANOPOLYSILOX MIXTURES AND APPLICATION FOR IMPREGNATION. - Google Patents

Description

The present invention relates to organopolysiloxane mixtures which can be cross-linked in thin layers by means of a hydrosilylation reaction suitable for impregnation of soft materials such as textile fibres, paper, cardboard, plastic materials, metal foils and the like, in particular to make these materials non-sticky to adhesives.

Mixtures of the above type have been known for a long time within the silicone industry and are described in detail in numerous patent documents and patent applications.

These mixtures are divided into three large families, namely mixtures without solvent, mixtures in solution in an organic solvent which is miscible with the silicones, and mixtures in aqueous emulsion.

These three families of mixtures entail analogous systems for crosslinking, namely: at least one organopolysiloxane containing per molecule at least two vinyl groups each linked to a silicon atom,

hereinafter referred to as "the SiVi group",

at least one organohydrogen polysiloxane containing per molecule at least three hydrogen atoms, each of which is linked to a silicon atom, referred to in the following as "group SiH",

a catalytically effective amount of a compound of a platinum group metal that catalyzes the hydrosilylation reaction.

These mixtures are generally available before use in at least two packages or two components, where the first component in principle contains the organopolysiloxane with the group SiVi and the hydrosilylation catalyst, while the second component contains the organohydrogenpolysiloxane, the two components being mixed at the same time as use.

In mixtures in an aqueous emulsion, or in solution in an organic solvent, it is well known that the water or the organic solvent at normal temperature plays an inhibitory role towards the platinum catalyst, as this effect disappears when the water or solvent evaporates at the time of the crosslinking treatment . This inhibitory effect allows inhibiting the formation of a gel at ordinary temperature at the time of their use by mixing the two components, since users after mixing the two components require a "use life" or "bath life" sufficient for a time of at least several hours, even several days.

The solvent-free mixture further necessarily comprises a fourth component which is generally termed an inhibitor of the hydrosilylation catalyst added together with one of the two components of the mixtures in an amount effective to inhibit the immediate formation of a gel at ordinary temperatures by the simultaneous mixing of the two components and impregnation of the supports, but then in an amount insufficient to prevent the hydrosilylation reaction during the crosslinking treatment. Such an inhibitor can optionally be used in mixtures in an aqueous emulsion or in a solvent mixture. The cross-linking treatment necessarily entails on the one hand evaporation of the water or the organic solvent for mixtures in aqueous emulsion or in solution and on the other hand a rapid and complete cross-linking of the mixture on its support by the hydrosilylation reaction.

This cross-linking reaction then entails an energy input which, for mixtures in emulsion and solution, necessitates a thermal treatment at 80 - 150°C, possibly combined with a specific treatment with UV rays, infrared radiation, ionizing radiation, corona effect, electron beams, etc.

US-A-3,328,482, US-A-3,527,659, US-A-3,814,731 and GB-A-1,240,520 can be particularly mentioned as patents illustrating mixtures in solution in an organic solvent.

US-A-3,445,420, US-A-3,527,659 and US-A-3,900,617 can be mentioned as patents illustrating mixtures in aqueous emulsion.

GB-A-1,041,082, GB-A-1,374,792 and US-A-4,043,977 and US-A-4,184,006 can be mentioned as patent documents illustrating mixtures without solvent.

Otherwise, the organovinyl cyclopolysiloxanes, and especially the methylvinyl cyclopolysiloxanes, have been used and known for a long time for dissolving platinum compounds in organopolysiloxane mixtures and inhibiting the activity of the catalyst at normal temperature in the hydrosilylation reaction. One can particularly mention FR-A-1,313,846 and supplement 88,676 for platinum halide, US-A-3,419,593 for chloroplatinic acid, US-A-3,715,334, 3,775,452 and 3,814,730 for a platinum compound containing at least one gram atom halogen per gramatom platinum.

Furthermore, in FR-A-2,232,575 and European patent application EP-A-146,422, the possibility of mainly using the vinyl-containing tetramer 1,3,5,7-tetramethyl 1,3,5,7 in mixtures such as organovinylcyclopolysiloxanes -tetravinyl-cyclotetrasiloxane.

However, no document is known which describes or proposes the use of a trimerized vinyl organocyclotrisiloxane and the special advantages that follow from this use.

In mixtures of the above type, the fundamental problem which is most difficult to solve is to arrive at a mixture which, after mixing the two components, leads to an improved compromise between stability (ie "use life" or "bath life") and the reactivity (i.e. short cross-linking time) in order to arrive at an effective and complete cross-linking during the cross-linking treatment.

One of the objects of the present invention is detailed to propose a crosslinking accelerator which does not affect the length of the service life, which accelerates the catalytic action of the hydrosilylation catalyst in the crosslinking treatment even in the presence of an inhibiting agent.

In the following, all percentages and parts by weight are on a weight basis unless otherwise stated.

This purpose is achieved by the present invention which concerns an organopolysiloxane mixture which can be cross-linked in a thin layer by hydrosilylation reaction and suitable for impregnation of soft materials, characterized in that it comprises: A) at least one organopolysiloxane containing per molecule at least two groups SiVi, B) at least one organohydrogen polysiloxane containing per molecule at least three groups SiH, C) a catalytically effective amount of a hydrosilylation catalyst which is a compound of a metal in the platinum group, the mixture being characterized by between 0.5 and 60%, and preferably between 1.5 and 20% of the number of groups SiVi in the mixture is added with a vinyl cyclotrisiloxane of formula:

in which R is selected from C 1 -C 4 alkyl radical, phenyl radical and 3,3,3-trifluoropropyl radical, with R preferably being a methyl radical.

The present invention has surprisingly and unexpectedly allowed the demonstration that the compound of formula (1) plays the role of crosslinking accelerator, i.e. accelerates the catalytic effect of the catalyst (C) in the crosslinking treatment without having affected the duration of the service life of the mixture. This role for the accelerator occurs when the mixture is in the form of an aqueous emulsion, a solution in an organic solvent which is miscible with the silicones and even in the case of a mixture without solvent and which also necessarily includes a fourth component (D) which is an inhibitor for the catalyst (C) added in an amount effective to prevent the formation of a gel at ordinary temperature, this amount being insufficient to prevent the hydrosilylation reaction in the cross-linking treatment.

The starting organopolysiloxanes (A) are diorganopolysiloxanes with the formula:

in which n and m are whole numbers which can each be zero, but where the sum has a value such that the organopolysiloxane has a viscosity at 25°C of at least 20 mPa.s and at most 30,000,000

mPa.s, the radicals R are the same or different and have the meaning given above in connection with formula (1) and R' is R or a vinyl radical, it being understood that if m = 0 then R' a vinyl radical.

The organopolysiloxanes (A) can also preferably include diorganocyclosiloxanes with the formula:

where R has the same meaning as in the preceding and p is an integer between 4 and 10.

The organopolysiloxanes (A) with formulas (2) and (3) are well known and are particularly described in US-A-3,220,972, US-A-3,344,111 and US-A-3,436,366, as these patents likewise describe the organohydrogen polysiloxanes (B).

Preferably, at least 60 mol% of the radicals R are methyl radicals and preferably all the radicals R are methyl radicals. The organohydrogenpolysiloxane (B) can be linear, cyclic or branched.

The mainly linear or branched organohydrogenpolysiloxane (B) has units of medium general formula:

in which the radicals R are the same or different and have the above meaning, but the possibility that some radicals R represent vinyl radicals is not excluded. Preferably, at least 80% of the radicals R are methyl radicals.

The symbol x stands for any number from 1 to 1.99, the symbol y stands for any number from 0.1 to 1, the sum of x + y being from 1.7 to 2.6. The methylhydrogenpolysiloxanes are preferably used as organohydrogenpolysiloxanes (B).

The organohydrogen polysiloxanes (B) can be obtained on the silicone market, but otherwise the production methods are well known. One of the most used methods consists in co-hydrolyzing in a first step suitable mixtures consisting of chlorosilanes selected from chlorosilanes with formulas: R^SiCl, R2SiCl2<

RSiCl3, SiCl4, HR2SiCl, HRSiCl2, HSiCl3. With pas-

sending mixtures shall be understood as mixtures which per silicon atom contains a number of radicals R and a number of hydrogen atoms coinciding respectively with the values represented by the symbols x and y and the general average formula, as the sum of these numbers must likewise coincide with the permitted values for the sum x + y.

In another step, the cohydrolysates are brought to a temperature of 80 to 220°C, preferably in the presence of acidic agents such as sulfuric acid, oxides activated with an acid. During the heating, there is a rearrangement of siloxane bonds as well as condensation of SiOH groups. These transformations lead to organohydrogen polysiloxane polymers (B) which, as a function of the starting mixtures of chlorosilanes, have linear, cyclic or branched structures.

Among the linear polymers, the linear polymers with the following formulas can be mentioned for illustrative purposes:

wherein the symbol g represents any number from 3 to 120, h represents any number from 1 to 50, p represents any number from 6 to 60, p' represents any number from 1 to 15 , q represents any number from 1 to 10 and q' represents any number from 7 to 40.

These linear polymers generally have a low viscosity graded e.g. from 5 mPa.s to 500 mPa.s at 25°C.

Among the cyclic polymers, for illustrative purposes, cyclic polymers corresponding to the following formulas can be mentioned:

With respect to the branched polymers, they are each composed of a combination of units selected from units of formulas R3SiOQ5,R2SiO, RSiOx5,SiO2,HR^IO<q>5<>>

HRSiO, HSiO^ j. , with each combination that defines a polymer containing at least one unit selected from units with the formula RSiO^ si02'HSioi 5. The units are distributed so that the average formula, branched at a silicon atom, for each polymer is covered by the previously mentioned general means formula.

The viscosity of these polymers is from 2 mPa.s at 25°C to 10,000 mPa.s at 25°C.

Concrete examples of branched polymers with low viscosity can be mentioned:

- polymers corresponding to the following formulas:

- polymers consisting of units SiG^ and H(CH^)^

SiO 5 with a CH3/Si ratio of 1 to 1.5.

In general, the components (A) and (B) are present in the mixture in amounts such that the ratio between the number of groups SiH and groups SiVi is between 0.5 and 5, preferably between 0.6 and 2.5.

In applications such as coating and more particularly in applications for anti-stick properties of paper, 0.5 to 50 parts by weight of polymer (B) can be used for 100 parts by weight of polymer (A).

One can use as catalyst (C) compounds of a metal in the platinum group, in particular their salts and complexes, in particular platinum olefin complexes as described in US-A-3,159,601 and US-A-3,159,662, reaction products of platinum derivatives with alcohols, aldehydes and ethers described in US-A-3,220,972, platinum vinyl siloxane catalyst described in FR-A-1,313,846 and Supplements 88,676 and FR-A-1,480,409, siloxane-ligand complexes described in US-A-3,715,334, US-A -3,775,452 and US-A-3,814,730 and organic ligand complexes described in European patents EP-A-57 459, EP-A-188 978 and EP-A-190 530, as well as rhodium catalysts as described in US-A- 3,296,291 and US-A-3,928,629.

The preferred metals in the platinum group are platinum and rhodium. Rhodium is also usable although it is less active but cheaper.

Generally, 5 to 200 ppm of catalyst is used, calculated on the metal weight in relation to the weight of the polysiloxanes with SiVi and SiH.

In the case where the mixture is used without a solvent, the viscosity of the polymer (A) and (B) is chosen so that the viscosity of the mixture, i.e. the composition, is between 40 and 5,000 mPa.s, preferably between 100 and 3,000 mPa.s at 25°C.

In this case, the mixture also contains an inhibitor (D) which may in particular be alkylthioureas (US-A-3,188,299), triallyl isocyanurates (US-A-3,882,083), dialkylacetylenedicarboxylates (US-A-4,347,346), diallyl maleate (US-A-4,256,870), organic acetylene compounds (US-A-3,445,420 and European patent application EP-A-146,422).

The amount of inhibitor used is generally between 0.01 and 3%, preferably between 0.05 and 2%, in relation to the total weight of the mixture.

The mixtures in accordance with the invention can be emulsified, dispersed or diluted in water or in a volatile organic solvent which is miscible with the mixture, selected e.g. among alkanes, petroleum fractions containing paraffin compounds, toluene, heptane, xylene, isopropanol, methyl isobutyl ketone, tetrahydrofuran, chlorobenzene, chloroform, 1,1,1-trichloroethane, derivatives of monoethylene glycol and methylene glycol.

Preferably, the water or solvent at the time of use constitutes 50 to 99% by weight of the dispersion or solution.

During the cross-linking treatment, which entails evaporation of the water or solvent from the dispersion, the mixture hardens and these dispersions are consequently usable as coating mixtures for soft carriers of metal, paper, plastic material, cardboard.

etc.

Mixtures in accordance with the invention are preferably used as mixtures to make a material non-sticky, such as e.g. metal foils, glass, plastic materials or paper, compared to other materials to which they usually stick.

The invention also relates to a method for making foils of soft material non-adhesive to surfaces to which they otherwise usually stick, and the peculiarity of the method consists in applying an amount of the mixture in accordance with the invention, generally comprising between 0.1 and 10 g per m<2>surface to be impregnated and to cross-link the mixture by supplying energy as stated above.

The gel formation time for these possibly diluted mixtures at normal temperature can be over 5 hours, but usually several days and the catalyst is reactive at higher temperatures, generally above 80°C, and is usually between 90 and 150°C.

The mixture without solvent, i.e. undiluted mixtures, is applied using devices suitable for the uniform application of small amounts of liquids. For this, you can use e.g. the device called "Helio glissant" comprising in particular two cylinders arranged one above the other. The bottom cylinder, which is immersed in the impregnation container where the mixtures are located, impregnates a very thin layer on the top cylinder, as this acts to the paper to deposit the desired quantities of the mixtures with which it is impregnated, such a quantity being achieved by regulating the respective speeds of the two cylinders which rotate in opposite directions in relation to each other. The impregnation machine described in French patent document 2,294,765 can also be used.

The diluted mixtures, i.e. with solvent or in aqueous emulsion, can be applied using devices used on industrial machines for impregnating paper such as the embossed cylinder "Mille points", the system called "Reverse Roll". When they are placed on the supports, the mixtures are cured by supplying energy, at least a part of which can be supplied with UV irradiation, for a few seconds by circulating under UV lighting and through tunnel ovens heated at 60 - 200°C. The passage time through these ovens generally varies from 2 to 30 seconds. It is a function of the length of the ovens, the speed at which the impregnated carriers pass through the oven (this speed can exceed 200 meters per minute).

The amounts of the mixtures that are deposited on the supports are variable and most often range from 0.1 to 10 g/m<2> of treated surface. These amounts depend on the nature of the carriers and the desired anti-adhesive properties. They are most often between 0.5 and 1.5 g/m<2>for non-porous supports.

The products with formula (1) are well-known products with manufacturing methods particularly described in US-A-3,607,898, US-A-3,763,212, US-A-3,989,733 and Japanese published patent application KOKAI 74/124 067 , mentioned as references.

The products with formula (1) lead to hard, yet soft coatings and this greatly facilitates the automatic mechanical cutting of soft compositions, especially papers, without changing the anti-stick effect.

Mixtures in accordance with the invention further contain, preferably in the mixtures without solvent, additives usually used, especially in small amounts, e.g. 0.1 to 5 parts by weight for 100 parts by weight of component (A) of an alpha-omega-dihydroxydimethylpolysiloxane oil with viscosity between 1 and 100 mPa.s at 25°C and with a weight content of OH between 1 and 10%.

Of course, mixtures in aqueous emulsion can be arranged generically in a part (I) containing (A) and (C) and a part (II) containing (B), comprising common emulsifiers or dispersants which can be anionic, non-ionic or cationic .

The non-ionic polymer materials such as polyvinyl alcohol ("RHODOVIOL" 25/140 from RHONE-POULENC, or "ELVANOL" 50-42 from DUPONT) is particularly suitable for part (I).

Otherwise, allyl ethers and allylphenyl ethers of polyalkylene glycols (e.g. "CEMULSOL" O.N. 10-20 from RHONE-POULENC or "TERGITOL" NP-40 from UNION CARBIDE) are particularly suitable for the part

(II).

In the following, all viscosities are measured at 25°C.

Example 1: demonstration of the high reactivity of the vinyl trimer.

The high reactivity of the vinyl trimer D^Vi in relation to the tetramer D^Vi and the pentamer D^Vi corresponding respectively to the above-mentioned formula (1) with R = methyl and formula (3) in the above with R = methyl and p = 4 and 5 respectively, are detected using DSC ("Differential Scanning Calorimetry") defined by ICTA ("International Congress of Thermal Analysis").

In this method, the enthalpy of the hydrosilylation reaction of a sample is assessed by subjecting this sample to a special thermal treatment.

The tested sample is a solvent-free mixture analogous to a mixture useful for the anti-stick treatment of paper comprising the following components: A) a random copolymer of dimethylvinylmethylpolysiloxane with dimethylvinylsiloxyl terminals at 3% by weight

vinyl group and a viscosity of 250 mPa.s

B) a methylhydrogenpolysiloxane copolymer with trimethylsiloxyl terminals containing 1.5% by weight of hydrogen atoms linked to silicon and having a viscosity of

20 mPa.s

- C) D_,Vi, D.Vi or DcVi.

3 ' 4 5

All mixtures comprising an additional 30 parts per million

_4

of platinum metal (1.5 10 g atom Pt/kg mixture) in the form of a platinum complex prepared from chloroplatinic acid and 1,3-divinyl-1,1,3,3-tetramethyl-disiloxane as described in US-A-3,814,730 .

The compositions of the four tested samples are collected in table I, where the content of components (A) to (D) is indicated as % by weight.

The four samples (10 mg each) are successively placed in a vessel which is cooled very quickly to -50°C under nitrogen and the sample is heated progressively with a steady temperature increase of 10°C per minute to 250°C while recording the released amount of heat and from the obtained curve is derived by integrating the reaction enthalpy (in Kcal/mol SiH).

The test results are collected in table II below, from which it appears that the temperature (T) for the exothermic peak is lower for D^Vi and this shows that the reaction is more exothermic for D^Vi. The reaction enthalpy is maximum for D^Vi. This shows the accelerator effect of D^Vi on the platinum catalyst in the hydrosilylation reaction.

If you reach all the reactive sites, you get a theoretical enthalpy of 25.8 Kcal/mol SiH.

- COMPARATIVE EXAMPLES 1 AND 2 and EXAMPLES 3 TO 6:

- aqueous emulsion :

a) but intimately mixes the following constituents :

- 100 parts of a dimethylmethylhydrogenpolysiloxane copolymer blocked at each end of the chain with a trimethylsiloxyl group and simultaneously containing dimethylsiloxyl units and methyl-hydrogensiloxyl units distributed statistically and alternately in the silicone chain, with viscosity 60 mPa.s at 25°C. 8 parts of a mixture in the weight ratio 70/30 of two polyoxyethylenated nonylphenols, one of which has 10 units of OCH2-CH2 and the other 20 units of OCh^-CF^, sold by RHONE-POULENC under the trade name "CEMULSOL" O.N. 10-20,

15.4 parts water

0.5 parts of an aqueous 40% acetic acid solution.

This mixture is emulsified by passing it through a colloid mill. The emulsified product is diluted by adding 43 parts of water.

The obtained emulsion contains a total of 60% of the hydrogen-organopolysiloxane.

b) intimately mix the following ingredients:

- 23 1 parts water

20 parts polyvinyl alcohol with a saponification number of 140 and which in 4% solution in water has a viscosity of 25 mPa.s at 25°C, sold by RHONE-POULENC under the trade name "RHODOVIOL" 25/140. Then add to this mixture: - 1.5 parts of a mixture in the weight ratio 70/30 of the two polyoxyethylenated nonylphenols used under a), - 350 parts of a statistical dimethylmethylvinylpolysiloxane copolymer with vinyl units in the chain and with vinyl -dimethylsiloxyl terminals with a viscosity of approximately 500 mPa.s

at 25°C and about 3% vinyl groups,

- 4 parts of a dimethylpolysiloxane blocked at each chain end with a dimethylvinylsiloxyl group and with a viscosity of 5 mPa.s at 25°C and with approximately 30% by weight of vinyl radicals, - 0 to 10 parts of tetramethyltetravinylcyclotetrasiloxane (Vi).

0 to 1 part trimethyltrivinylcyclotrisiloxane (D^Vi) is added to this mixture. The entire mixture is then emulsified by passing it through a colloid mill. The emulsified product is diluted with the addition of 292.5 parts of water and in the diluted emulsified product is incorporated by simple stirring:

70 parts emulsion prepared under a),

20 parts monopropylene glycol.

The aqueous emulsion mixture formed in this way is very stable on storage. In particular, it does not show any particular loss of SiH groups after a period of 6 months at 40°C in a closed container.

100 ppm of platinum (5.10 ^ gram atoms of platinum per kg mixture) is added to this emulsion in the form of a complex of platinum prepared from chloroplatinic acid as described below.

A platinum triene complex is prepared by mixing:

- 1 part H2PtCl6, 6H20,

5 parts isopropanol,

2 parts sodium bicarbonate NaHCO^ , and

6 parts yd-myrcene.

The chloroplatinic acid is first dissolved in isopropanol, then NaHCO^ is added in small portions to avoid the formation of foam during the release of carbon dioxide gas, after which

The ^-myrcene is added.

The mixture is refluxed for 20 minutes at approximately 80°C with stirring. The initial orange color changes to yellow. The reaction mixture is cooled to normal temperature and isopropanol is removed at 20°C under a vacuum of 1.5 KPa. Inorganic impurities are removed in hexane and, after filtration, the solution is concentrated at 40°C under a vacuum of 0.1 to 1 KPa. An organ red oil is obtained in a yield of 80% in relation to the total weight of platinum and starting reaction components. A ratio CL/Pt = 1.0 is achieved. The concentration of the complex is lowered to 3% by dilution in toluene. It is this resolution that is used in the following.

This complex is used in the form of an aqueous emulsion containing 2% polyvinyl alcohol as indicated under b).

The mixture is stirred vigorously at room temperature for a few minutes.

This catalyzed emulsion is then diluted by the addition of a sufficient quantity of water to form a treatment bath of 10% solids content.

This bath is deposited in an amount of 8 g/m<2>on a kraft paper with a basis weight of 50 g/m2, satin on the surface.

The deposition is carried out with the aid of a Mayer galling rod mounted on an industrial paper coating machine.

The emulsion film covering the paper is dried and simultaneously cured by passing for X seconds through a heated tunnel oven, the temperature in the paper being 110°C, to determine the crosslinking time.

A coated paper is then obtained which on one side has approximately 0.8

g/m<2> of a thin fully cross-linked coating.

On the impregnated surface of the paper treated according to d), an adhesive tape (pressure sensitive designated "TESA" 4651) is applied and this application is maintained for 20 hours under a pressure of 70 g/cm 2 . The force required to tear off this band is then measured using a dynamometer, the speed of the tear being 30 cm/minute. A tear-off force of 10 g is found for a band width of 1 cm. If a tear-off speed as high as 300 m/minute is used, there is a tear-off force of 40 g for a belt width of 1 cm.

To assess the stability of the catalyzed bath, a new impregnation is carried out under the same conditions using a treatment bath that has been aged for 24 hours. The stability of the bath is judged to be good if the cross-linking time during the impregnation at 110°C and if the anti-stick effect achieved are identical to those achieved at time 0 of the bath's service life.

In the following table III, the acceleration of the cross-linking due to the trimethyltrivinylcyclotrisiloxane is shown without any detrimental effect on the stability of the bath (24 hours).

- COMPARISON EXAMPLE 7 AND EXAMPLES 8 AND 9:

mixture without solvent :

A treatment bath is produced using the following working method:

a) - 1000 parts of a silicone mixture containing:

894 parts of a copolymer of polymethylvinyldimethylsiloxane with vinyl units in the chain and dimethylvinylsiloxyl terminals with about 3% by weight of vinyl groups and a viscosity of about 250 mPa.s at 25°C. b) - 25 parts of 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl-cyclotetrasiloxane (D^vi), c) - 70 parts of a liquid polymethylhydrosiloxane with trimethylsilyl terminals used as a cross-linking agent containing approx. 1.5% by weight of hydrogen atoms linked to silicon, with a viscosity of approximately 20 mPa.s at 25°C, d) - 10 parts of an alpha-omega-dihydroxydimethylpolysiloxane oil with a viscosity of 50 mPa.s at 25°C and a content of hydroxyl groups of 4%, e) - 1 part 8-chloro-1-octyn-3-one (inhibitor for Pt) certain synthesis is described in EP-A-146 422.

One adds to this bath:

- 0 to 3 parts 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane (D, Vi ), -4 - 60 ppm platinum (3.10 g.at Pt/kg mixture) in the form of a platinum complex prepared from chloroplatinic acid and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane as described in Example 1 of US-A-3,814. 73 0 .

The mixture is stirred vigorously at normal temperature for a few minutes and the minimum time for the initiation of the cross-linking process is measured on a hot plate at 100°C (in seconds) according to standard NF 3 0-506, the sample portion being limited to 0.2 g. The results are summarized in Table IV.

Table IV clearly shows the effect of the crosslinking accelerator Vi. - EXAMPLES 10 TO 14 AND COMPARATIVE EXAMPLE 15:

Mixing in organic solvent :

a) - 1000 parts of a silicone mixture containing:

<*>3 00 parts of a polyvinylmethyldimethylsiloxane rubber with vinyl units in the chain and trimethylsiloxyl terminals with about 0.07% by weight of vinyl groups and with a viscosity of about 20.106 mPa.s at 25°C,<*>7 parts 1.3 , 5,7-tetramethyl — 1,3 ,5,7-tetravinylcyclo-tetrasiloxane (Vi ),<*>8 parts of a hydrogenmethyldimethylpolysiloxane copolymer containing methylhydrogensiloxyl units and dimethylsiloxyl units and with trimethylsiloxyl terminals of about 1 wt. % hydrogen atoms linked to silicon and a viscosity of about 45 mPa.s at 25°C,

<*>685 parts toluene.

One adds to this bath:

0 to 1 part trimethyltrivinylcyclotrisiloxane ( D.. Vi ),

60 ppm platinum (3.10 g.at Pt/kg mixture) in form

of a platinum complex prepared from chloroplatinic acid and 1,3-divinyl, 1,1,3,3,-tetramethyldisiloxane as described in e.g. US-A-3. 8 1 4 . 73 0 .

The mixture is stirred vigorously at ordinary temperature for a few minutes and then the mixture is deposited (about 1 to 3 g/m2 ) on paper using an impregnation knife blade and the silicone mixture is cured in a forced air oven regulated at 110°C.

One then studies the curing of the silicone coating by noting (in seconds) the minimum residence time in the oven (the curing time) necessary to achieve a thoroughly cured coating. One then measures the increase in viscosity as a function of the time for the catalyzed bath to determine (in hours) the stability of the bath (the bath's useful life). The time for gel formation of the catalyzed mixtures is also measured at 60°C (in minutes) in accordance with standard NF 51-429 (December 1983).

The results obtained are collected in table V below, where it appears that D^ Vi has an accelerating effect on the cross-linking without affecting the stability of the bath.

Claims (8)

1. Organopolysiloxane mixture which can be cross-linked in a thin layer by hydrosilylation reaction, suitable for impregnation of soft materials, characterized in that it includes: - A) at least one organopolysiloxane containing per molecule at least two groups SiVi, - B) at least one organohydrogen polysiloxane containing per molecule at least three groups SiH, - C) a catalytically effective amount of a hydrosilylation catalyst which is a compound of a metal from the platinum group, characterized in that between 0.5 and 60%, and preferably between 1.5 and 20% of the number of groups SiVi in the mixture are added using a vinylcyclotrisiloxane of formula: in which R is selected from C2~C4 alkyl, phenyl and 3,3,3-trifluoropropyl, preferably methyl. 2. Mixture as stated in claim 1, characterized in that Ri formula (1) is methyl. 3. Mixture as stated in claim 1 or 2, characterized in that it is without solvent, the viscosity of the components (A) and (B) is chosen so that the viscosity of the mixture is between 40 and 5000 mPa.s and that the mixture further contains: - D) an inhibitor in an effective amount to inhibit the formation of a gel at ordinary temperature, but provides a sufficient amount to prevent the hydrosilylation reaction in the cross-linking treatment. 4. Mixture as stated in claim 1 or 2, characterized in that it is dispersed in an organic solvent which is miscible with the silicones. 5. Mixture as stated in claim 1 or 2, characterized in that it is in the form of an aqueous emulsion. 6. Mixture as specified in claims 1 to 5, characterized in that it further comprises 0.1 to 5 parts by weight per 100 parts by weight of component (A) of an alpha-omega-dihydroxydimethylpolysiloxane oil with viscosity between 1 and 100 mPa.s at 25°C and with a weight content of OH between 1 and 10%. 7. Procedure for making foils of soft materials non-sticky to surfaces to which they normally stick, characterized in that an amount of between 0.1 and 10 g per m <2> surface to be coated is applied a mixture as specified in any of claims 1 to 6 to cross-link the mixture. 8. Soft materials impregnated with a cross-linked composition as defined in any of claims 1 to 6.