Imported: 10 Mar '17 | Published: 27 Nov '08
USPTO - Utility Patents
Silicone coating on various soft supports, for instance textiles, made of synthetic polymers (polyamide, polyester) provides an efficient method for producing water impermeable and water permeable coatings, on soft supports, said method enabling to improve permeability to water vapor of the silicones while preserving impermeability to water. The inventive method enabling this consists mainly in: coating one of the surfaces of the support with a film formed by an invert water-in-oil silicone emulsion comprising a continuous oily silicone phase phi s, crosslinkable into elastomer and including a polyorganosiloxane (POS) A crosslinkable by addition polymerization, by cationic process or free-radical process; optionally a crosslinking organosilicon compound B; and optionally at least a catalyst C; an aqueous phase phi a; a stabilizing agent; and in ensuring crosslinking of the silicone phase phi s and elimination of water. The invention also concerns water impermeable and water vapor permeable soft polyamide or polyester substrates obtained by using an invert water-in-oil silicone emulsion.
The invention relates to the general field of silicone coating on various pliable supports, for example textiles, made of synthetic polymers (polyamide, polyester, etc.).
More precisely, the invention relates to the coating of pliable (or flexible) materials with liquid compositions containing one or more polyorganosiloxanes (POS) that are crosslinkable by polyaddition, by polycondensation, by cationic means or by free-radical means, so as to form a protective film or coating having especially breathable waterproof (permeable to moisture vapour but impermeable to water) and/or hydrophobic properties.
The pliable supports, in particular textile supports, which can be coated with films made of crosslinked silicone elastomers are, for example, fabrics for clothing.
The web of pliable supports is coated on at least one of its faces with a silicone film which can be crosslinked, with the aid of means for activating the crosslinking arranged downstream of the coating head. These means for activating the crosslinking can be heat emitters, radiation (e.g. UV) emitters or electron beam emitters, inter alia.
In the clothing industry, technical fabrics industry or furniture industry, there exists a constant need for materials which do not allow water, but only moisture vapour, to pass through. Being protected against water, whether it comes from the outside, such as rainwater, or from the inside, such as moisture vapour from perspiration, destined for rapid condensation, is in fact a particularly important element of comfort for users. To avoid this coming into contact with water, the textile barrier should allow rapid evacuation of the endogenous water when it is in vapour form before it condenses, and should oppose the penetration of the exogenous water, even when said water is under (slight) pressure.
Besides its performance levels of impermeability to liquid water and of breathability with respect to moisture vapour, other properties are required for the pliable supports, in particular textiles, namely in particular: permeability to air, beading effect, etc.
In order to be able to be breathable waterproof, a pliable support must be pierced with millions of quite small pores so as not to allow droplets of water to pass through but only to allow water in the form of vapour to pass through.
Two techniques are used to obtain this property: laminating and coating.
Laminating consists in laminating a porous very fine membrane onto the outer layer of the piece of clothing (2 layers) or between the outer layer and the lining (3 layers, for example GORE).
Moreover, coating consists in passing a coating over the piece of clothing, on which microholes will allow moisture vapour to pass through. The coating film may, for example, be made of microporous polyurethane.
A certain number of patents exists which relate mainly to microporous breathable waterproof pliable supports (membranes), that are waterproof and permeable to moisture vapour, made of expanded polytetrafluoroethylene (for example U.S. Pat. No. 5,948,707; U.S. Pat. No. 4,187,390; U.S. Pat. No. 3,953,566; U.S. Pat. No. 4,194,041; WO-A-99/39038), or based on polyurethane (for example EP-A-0 503 826).
Silicones are used in these productions comprising microporous breathable waterproof membranes.
Firstly, the involvement of the silicones can be to form coatings which make the supports impermeable. This is illustrated by EP-A-0 503 826, which describes novel organosilicone compounds, neopentasiloxanes, Si(OSiR2Q)4 with Q consisting of ethylene oxide and/or propylene oxide units, and the use of these silicones in the formation of a film that is waterproof and permeable to moisture vapour. In fact, polyurethane membranes suffer from a low resistance to abrasion and a loss of waterproofness when the permeability to moisture vapour increases. According to EP-A-0 503 826, the use of these organosilicone compounds as co-ingredients in the polyurethane coatings makes it possible to increase the performance levels of the latter.
As described in WO-A-01/26495, silicones can also be used to impermeabilize seams.
According to U.S. Pat. No. 5,948,707 silicones can contribute to improving the mechanical properties of microporous breathable waterproof membranes. This patent relates more precisely to an expanded PTFE membrane in which one of the faces is covered with a discontinuous elastomeric coating which introduces non-slip properties by substantially increasing the friction coefficient.
WO-A-91/17205 discloses the use of crosslinkable or non-crosslinkable elastomeric silicones for producing interpenetrating matrices of PTFE resin and of silicone and thus improving the physical characteristics of the material. These structures are microporous, waterproof and permeable to moisture vapour, with improved physical characteristics and resistance to detergents. The silicone penetrates inside the pores, producing a coating of the nodes interconnected by fibrils and of the fibrils themselves.
It emerges from this review of the state of the art that it is unknown to use a silicone elastomer, and even less so a water-in-silicone oil emulsion, as essential constituent material of microporous pliable supports that are waterproof and permeable to moisture vapour.
Nevertheless, the known microporous breathable waterproof ready-made garments comprising silicone can still be improved as regards their waterproofness and their moisture vapour-permeability, while at the same time satisfying economic constraints.
Moreover, improvements are always desirable in economic terms and in terms of industrial operating conditions: ease of implementation/hygiene and safety.
Under these circumstances, an essential aim of the invention is to propose an effective process for producing coatings that are waterproof and permeable to moisture vapour, on pliable supports, this process allowing an improvement in the moisture vapour-permeability of silicones while at the same time conserving the waterproofness.
Another essential aim of the invention is to propose an economical, readily implemented and safe process for producing coatings that are waterproof and are permeable to moisture vapour, on pliable supports.
Another essential aim of the invention is to propose a novel silicone starting material for processes for producing coatings that are waterproof and permeable to moisture vapour, on pliable supports, this novel starting material having to be effective (waterproofness/moisture vapour-permeability) and economical, and easy and harmless to handle.
Another essential aim of the invention is to propose waterproof breathable silicone fabrics which are entirely effective and relatively expensive, and which can be manufactured under industrial conditions.
These aims, among others, are achieved by the present invention, which relates, first of all, to a process for producing coatings that are waterproof and permeable to moisture vapour, on pliable supports, characterized in that it consists essentially:
This therefore involves using a reactive, film-forming water-in-silicone oil inverse emulsion to coat a pliable support, for example a microporous membrane, for the purpose of forming, after crosslinking, a silicone elastomer coating which is itself also microporous.
The inverse silicone-based emulsions consist of droplets of water in a continuous silicone oil phase. The water-in-oil emulsions according to the invention do not comprise the water-in-silicone oil emulsions obtained from silicone elastomers in solution in organic solvents.
They can be obtained by means of emulsification processes well known to those skilled in the art and which involve mixing an aqueous phase a and an oily phase s without or with milling, i.e. with high shear.
Without wishing to be bound to the theory, the principle of this invention would therefore be as follows: when coated onto the support to be treated, the inverse emulsion constitutes a film. The oily phase of the emulsion is then crosslinked so as to form the coating and the aqueous phase is eliminated by evaporation (either during the crosslinking or by heating). The disappearance of the water then results in the formation of micropores in the silicone film. It is therefore necessary to use a reactive silicone oil.
Furthermore, the elimination of the water contained in the emulsion gives the fabric the breathability.
If the thickness of the coating is of the size of the particles, the evaporation of the water effectively creates pores, i.e. a direct contact between the outside and the inside of the fabric.
On the other hand, if the coating is thicker than the droplets of water, there will not, a priori, be this contact. However, it is then possible for percolation to occur and for pathways to be created during the evaporation and to thus allow the moisture vapour to pass through.
The silicone phase s preferably has a viscosity at 25 C. of less than 2000 mPas, preferably of between 100 and 1400 mPas, and even more preferably of between 100 and 800 mPas.
The aqueous phase a preferably comprises from 30 to 90% by weight of water, and even more preferably from 40 to 80% by weight of water.
As regards the mean particle size of the dispersed phase (water), it is chosen so as to confer a certain stability on the inverse emulsion. This mean particle size is not critical. It is preferable for this aqueous phase a to have a mean particle size defined by its mean diameter D50 (in m) such that:
For the purpose of the invention, the parameter D50 is the median size of the granulometric distribution. It can be determined on the graph of cumulative granulometric distribution, obtained by one of the analytical techniques mentioned below, by determining the size corresponding to the cumulation of 50% of the population of the particles. In practical terms, this granulometric parameter D50 corresponds to the mean maximum size of at least 50% of the mass of particles under consideration; a D50 of 10 m indicates that 50% of the particles are less than 10 m in size. The granulometric measurements can be carried out by conventional techniques such as sedimentation, laser diffraction (for example COULTER LSI30: with the proviso of using a cuvette suitable for this measurement), optical microscopy coupled to image analysis, etc.
The stabilizer is preferably chosen from the group comprising:
The surfactants are chosen more generally as a function of the HLB. The term HLB (hydrophilic lipophilic balance) denotes the ratio of the hydrophilicity of the polar groups of the surfactant molecules to the hydrophobicity of their lipophilic portion. HLB values are in particular reported in various basic manuals such as the Handbook of pharmaceutical excipients, The Pharmaceutical Press, London, 1994.
The water/silicone emulsions can also be stabilized via silicone polyethers (Silicone surfactantsSurfactant Science series V86 Ed Randal M. Hill (1999)).
Moreover, since the beginning of the century, solid particles are known to enable the stabilization of water-in-oil emulsions. The formation of a water-in-oil emulsion is promoted when the angle of contact between the oil, the solid and the water is greater than 0 C. The addition of a co-stabilizer can make it possible to improve the stability of emulsions. [Journal of colloid and interface science 213, 352-359 (1999)].
As regards the make-up of the continuous oily silicone phase s, it may, according to a first embodiment, be a composition of the type such as that which is crosslinkable by cationic means, in the presence of a photoinitiator and with actinic activation. More precisely, such a composition may comprise:
Even more preferably, the POSs A are epoxysilicones and/or vinyl ether silicones which are:
in which formulae:
According to a preferred characteristic of the invention, the initiators C are, for example: triarylsulphonium salts (for example: [aryl]3S+, PF6 such as that sold by the company Ciba Geigy under the name Cyracure PI UV 6990), or else the onium borates described in European patent application No. 0 562 922, the entire content of which is included in the present application by way of reference. Even more precisely, it is possible, in practice, to use the initiator having the formula below:
In practice, the initiators for the use according to the invention are prepared very simply by dissolving onium borate or an organometallic complex, preferably of onium, in the form of a solid (powder), in a solvent.
According to an alternative with regard to the onium borate, the latter can be prepared directly in the solvent, from a salt (e.g. chloride) of the cation (iodonium) and a salt (for example potassium salt) of the borate anion.
Preferably, it is envisaged in accordance with the use according to the invention that the initiator (PI) will be used in solution in an organic solvent, preferably chosen from solvents which are proton donors, and even more preferably from the following group: isopropyl alcohol, benzyl alcohol, diacetone alcohol, butyl lactate, esters, and mixtures thereof. As is claimed in French patent No. 2 724 660, organic solvents which are proton donors and which are aromatic in nature (benzyl alcohol), behave as crosslinking accelerators. It is therefore advantageous to use them to dissolve the photoinitiator.
It should be specified that the expression effective catalytic amount of PI is intended to mean, for the purpose of the invention, the amount that is sufficient to initiate the crosslinking.
In so far as, in practiceas indicated above, the photoinitiator is advantageously dissolved in a polar solvent, it is in an amount such that its titre in the solution obtained is between 1 and 50% by weight, preferably between 10 and 30% by weight, and even more preferably between 15 and 25% by weight.
According to an advantageous feature of the use according to the invention, the incorporation of the PI in solution into the oily silicone phase s is carried out at a rate of 0.1 to 10% by weight of solution relative to the final mixture, preferably 0.5 to 5% by weight, and more preferably of the order of 1% by weight.
In practice, the photoinitiator is thus often present in this oily silicone phase s before the emulsification. This photoinitiator can optionally play the role of co-surfactant.
In accordance with a second embodiment corresponding to a mode of crosslinking of the silicones by polyaddition, the following products are chosen as constituents of the silicone phase:
POS (A): product having units of formula:
in which Z has the same meaning as above and c has a value of between 0 and 3, for example between 1 and 3;
dimethylpolysiloxanes with dimethylvinylsilyl ends, copolymers of methylvinyldimethylpolysiloxanes with trimethylsilyl ends, copolymers of methylvinyldimethylpolysiloxanes with dimethylvinylsilyl ends and cyclic methylvinylpolysiloxanes being more specially selected;
POS (B): product having siloxyl units of formula:
in which L has the same meaning as above and g has a value of between 0 and 3, and (methylhydrosiloxy) (,-dimethylhydro)-poly(dimethylsiloxane) being more specially selected.
These POSs that are crosslinkable by polyaddition can be of the type such as those which crosslink at room temperature or under hot conditions by means of polyaddition reactions in the presence of a metal catalyst, in this case platinum-based. They are crosslinkable POS compositions referred to as RTV (room temperature vulcanizing) or cold vulcanizable elastomers (EVF).
However, it may be desirable, on an industrial level, to accelerate the crosslinking by increasing the temperature of the silicone layer deposited onto the pliable support (for example 100-150 C.)/tunnel oven in an industrial device functioning continuously. This involves the polyaddition POS compositions referred to as HVE, which is the abbreviation for hot vulcanizable elastomer.
The two-component or single-component POS compositions that are RTV or HVE by means of polyaddition, essentially by reaction of hydrosylyl groups on sylylated alkenyl groups, generally in the presence of a metal catalyst (preferably a platinum catalyst), are described, for example, in U.S. Pat. Nos. 3,220,972, 3,284,406, 3,436,366, 3,697,473 and 4,340,709.
According to a third embodiment, the silicone phase can crosslink by polycondensation of OH groups and/or of hydrolysable groups, in the presence of a tin catalyst. This is aimed at two-component or single-component POS compositions which crosslink at room temperature by means of polycondensation reactions under the action of moisture, generally in the presence of a metal catalyst, for example a tin compound (RTV polycondensation).
The POSs which go into making up these RTV polycondensation compositions are linear, branched or crosslinked polysiloxanes carrying hydroxyl groups or hydrolysable groups, for example alkoxy. Such compositions can also contain a crosslinking agent, which is, in particular, a cylinder carrying at least 3 hydrolysable groups, such as, for example, a silicate, an alkyltrialkoxysilane or an aminoalkyltrialkoxysilane.
These compositions are described, for example, in U.S. Pat. Nos. 3,065,194, 3,542,901, 3,779,986 and 4,417,042 and in patent FR-2 638 752 (single-component compositions) and in U.S. Pat. Nos. 3,678,002, 3,888,815, 3,933,729 and 4,064,096 (two-component compositions).
Besides these POSs, the liquid silicone coating composition can also contain:
As regards the additives (E), mention may be made of:
As regards the methodological characteristics, an amount of inverse silicone emulsion such that the thickness of the film forming the coating is less than or equal to 500 m, preferably between 150 and 300 m, is applied to the support.
According to another of its aspects, the invention relates to the use of a water-in-oil inverse silicone emulsion, comprising:
Also protected by the invention is any film-forming water-in-oil inverse silicone emulsion, for producing coatings that are waterproof and permeable to moisture vapour, on pliable supports, characterized in that it comprises:
Finally, another subject of the invention consists of a pliable support, preferably textile support, and even more preferably synthetic textile support, characterized in that it is coated on at least one of its faces with a coating that is waterproof and permeable to moisture vapour, obtained by implementing the process as defined above or according to the use as defined above, or else using the emulsion as defined above.
The support used in these experiments is made of polyamide (110 decitex).
The coating methods are well known to those skilled in the art.
Advantage of the coating based on the silicone oil inverse emulsion compared to the coating with silicone oil alone.
On a laboratory scale, the oil is introduced into an IKA-type reactor equipped with a scraper blade and a counter blade. The silica is introduced into the oil with stirring (80-100 rpm). After complete dispersion of the silica in the oil, the water is introduced slowly and the stirring is maintained until the water has been completely incorporated. When the stirring is stopped, no drop of water should be visible at the surface.
The stabilization is provided by a hydrophobic precipitated silica (for example Sipernat D10 from Degussa).
The photoinitiator is present in the oil before the emulsification, at a rate of 0.5% by weight, and combines 0.5% by weight of a cosolvent consisting of isopropanol. The photoinitiator used is that having the formula below:
In an MPC oven or air-conditioned room at 25 C. and 50% relative humidity, the coated support is placed in a leaktight manner over an aluminium crucible containing 150 ml of water, a drop of bactericide and a piece of sponge which makes it possible to avoid any contact between the membrane and the water. The crucible should be placed in the air-conditioned room or the oven for 48 h before measurements start to be taken. After equilibration, the crucible is weighed regularly every 24 hours.
The curve of the loss in mass as a function of time is plotted. This curve should be taken into account when it becomes linear. The permeability P can then be calculated in the following way:
P=slope/r2 expressed in g/m2/24 h
The results obtained are as follows:
Influence of the water content of the inverse emulsion:
In addition, this test was carried out in order to compare the permeability provided by emulsions containing various amounts of water: 20%, 30%, 45% and 60%. The emulsions are stabilized with 8% silica relative to the water.
The permeabilities thus obtained are as follows:
The permeability to moisture vapour was also evaluated at 38 C. and 50% RH.
The inverse emulsions used for the coating contain from 20 to 60% of water.
The results are as follows:
These results are reported in the attached FIG. 2.
The permeability to moisture vapour (23 C., 50% RH) was also tested on clothing fabrics containing cotton and polyester using an inverse emulsion containing 60% of water stabilized with 8% of silica/water.
Overall, the results were as follows:
All these results show that: