Patent Application
20090297719
The invention relates to the general field of the silicone coating, on high-speed rolls, of various flexible supports, such as sheets of paper or of synthetic polymer (polyolefin, polyester, etc), or else of textile.
More specifically the invention concerns the coating of flexible materials with liquid compositions comprising one or more polyorganosiloxanes crosslinkable by polyaddition, by dehydrocondensation, by polycondensation, cationically or free-radically to form a protective coating or film having, in particular, release and/or water repellency properties.
The flexible supports may be papers, cards, plastic films or metallic films. The applications of these silicone-coated supports are, for example: paper for food use (baking molds, wrapping), adhesive label/tape, packing and sealing material, etc.
The coating of these flexible supports with crosslinkable liquid silicones is carried out on coating devices which operate continuously and at very high speed. These devices comprise coating heads composed of a number of rolls, including in particular a press roll and a coating roll, which is fed continuously with crosslinkable liquid silicone composition, by means of a series of rolls which are associated with one another. The web of flexible support circulates at high speed between the press roll and the coating roll and is thereby coated on at least one of its faces with a silicone film which is intended to be crosslinked by crosslinking means disposed downstream of the coating head. These crosslinking means may be emitters of heat, of radiation (e.g., ultraviolet) or of electron beams, for example.
In the race for productivity, the producers of silicone release-coated flexible supports are customers for liquid silicone coating formulations which are suited to increasingly high linear running speeds of the flexible support web. The economic factor is obviously not insignificant in this search for new silicone formulations for high-speed coating.
Nevertheless, the high speeds on continuous coating machines are known to be a byword for problems of transfer of the liquid silicone film from the coating roll to the moving flexible support web. These transfer problems (“splitting”) are manifested, in particular, in the incidence of a mist or aerosol (“misting”, “fogging”) in the area around the coating head and, more particularly, at the points of contact between the rotating rolls and/or between the coating roll and the flexible support to be coated. The density of this mist or of this aerosol increases in line with the linear running speed and hence the speed of rotation of the rolls.
Consequences of this phenomenon are, first of all, a loss of consumable material, and in particular the deposition of droplets of coating liquid on the support downstream (for example, at the oven), which is seriously detrimental to the quality of the coating.
Moreover, this undesirable formation of mist has adverse consequences from the standpoints of industrial hygiene and of safety for the operatives, who are exposed to a high level of aerosol in the vicinity of the roll coating device. This aerosol may be toxic.
Furthermore, the misting gives rise to the rapid fouling of the roll coating device, causing maintenance constraints and premature wear.
To guard against the consequences of this mist, it is usual to dispose a suction withdrawal system around the coating head, allowing said mist to be captured.
Moreover, the skilled worker knows of a certain number of adjustments to the coating head in order to obviate this phenomenon. Some examples of this include:
Another approach for controlling the formation of mist in roll coating machines involves acting on the formulation of the liquid silicone coating composition.
In accordance with this approach, it is known to reduce the number-average degree of polymerization of the polyorganosiloxanes forming the silicone coating liquid and, consequently, to reduce the viscosity of the silicone coating bath so as to limit the density of the mist.
These known techniques are subject to a serious drawback, in that they substantially modify the properties and, in particular, the release of the flexible silicone-treated support it is desired to obtain.
To illustrate this approach, through the silicone formulation, it is possible to cite international patent application WO 2004/046248, which describes the use of star-branched silicone polymers used as an antimisting additive for coating applications on flexible supports. The process for preparing these star-branched silicone polymers comprises incompletely reacting (by hydrosilylation) a polyorganosiloxane containing reactive ≡SiH units with a long-chain olefin to give a partially substituted polyhydroorganosiloxane, which is subsequently reacted by hydrosilylation with a vinyl silicone resin of MQ type and a long-chain diolefin. It is clear that compositions of this kind are relatively complex and therefore costly to obtain. Moreover, they still remain capable of improvement in terms of controlling misting in high-speed silicone roll coating.
European patent EP-0 716 115 describes a process for preparing a silicone composition for high-speed coating with rolls, said composition being presented as permitting a reduction in mist density. According to this process, a trimethylsilyl-terminated polydimethylmethylhydrosiloxane with a degree of polymerization of 12, and also 0.01% of a polydimethylsiloxane which is substituted with perfluoroethylbutyl and methylvinyl functions, whose end groups are dimethylvinylsiloxy groups, and whose degree of polymerization is 300, and also polypropylene glycol and, optionally, a stearyl or oleyl alcohol are employed. This leads to polydimethylsiloxanes which are functionalized with polyoxypropylene groups. These functionalized polydimethylsiloxanes are combined with other functionalized polydimethylsiloxanes, functionalized for example with hexenyl units, and are also combined with a platinum-based hydrosilylation catalyst, to form silicone coating compositions which permit a reduction in mist formation. The functionalization units may be hydrophobic residues such as stearic or oleic acid residues.
The U.S. Pat. No. 4,808,391 relates to silicone-based inks and varnishes, and more specifically to a method of applying these inks/varnishes to a substrate, using a roller coating machine operating at high speed. This patent discloses, in particular, compositions comprising vinyl-terminated polydimethylsiloxanes with a viscosity at 25° C. of between 15 000 and 50 000 mPa·s. These liquid coating compositions further comprise a platinum-based catalyst and a Theological additive composed of silica with a high specific surface area, more particularly fumed silica.
The U.S. Pat. No. 6,057,033 discloses silicone compositions intended for coating on flexible supports to form, after UV-induced cationic crosslinking, a release coating. In addition to the polyorganosiloxanes, these compositions comprise cellulose fibers which have an average length of between 15 and 100 μm and an average thickness of between 5 and 40 μm. The polyorganosiloxanes employed are polyorganosiloxanes which are functionalized with crosslinking groups of acryloxy or methacryloxy type, allowing UV-induced free-radical crosslinking.
The cellulose fibers incorporated into the composition make it possible to provide a solution to the technical problem, which is that of obtaining a nonbrittle crosslinked silicone release coating. The cellulose fibers are presented as producing improvements with regard to the transfer of the silicone coating film to the support, resistance to die cutting, mechanical properties (tensile resistance and tearing resistance), the anchoring of the coating to the paper, the reduction of the absorption of the coating liquid within the paper, and, incidentally, the reduction of mist formation.
On this last point, U.S. Pat. No. 6,057,033 does not provide any quantitative element for assessing the reduction in mist to which the cellulosic fibers give rise. There is good reason to think that this reduction remains completely inadequate.
Also cited, for report, is Japanese patent application JP-62 64 011, which describes a coating liquid comprising a film-forming resin and a solvent and which further comprises wax particles with a diameter of between 1 and 10 μm, the diameter of the coarsest particle being not more than 150% of the thickness of the wet film coating applied to the support. A coating liquid of this kind would allow an increase in coating speed of at least 10 to 30 m/min, by virtue a priori of a limitation on the formation of mist. The teaching of such a document is remote since it does not relate to silicone coatings.
In the light of this prior art, one of the essential objectives of the invention is to provide an effective method of controlling misting when coating flexible supports with a liquid silicone composition which is a precursor of crosslinked coatings, said coating taking place with the aid of a roll coating device operating at high speed.
Another essential objective of the invention is to provide a simple and economic method of controlling misting when coating flexible supports with a silicone composition intended for crosslinking, said coating taking place in a roll coating device operating at high speed.
Another essential objective of the invention is to provide a new additive which makes it possible to reduce the formation of mist when coating flexible materials, at high speed on rolls, by means of silicone compositions which can be crosslinked to give release coatings.
Another essential objective of the invention is to provide a method of controlling misting in the context of the coating of flexible supports, with a silicone composition which can be crosslinked to give release coatings, using a roll coating device.
All of these objectives, among others, are attained by the present invention, which first provides a method of controlling misting when coating flexible supports, comprising the following steps:
a) preparing a liquid silicone composition X, a precursor of silicone coating(s), comprising:
The inventors are meritorious in having obtained effective control over mist formation, which is manifested in a signifi-cant amelioration of the problem associated with the incidence of said mist in a roll coating system operating at high speed.
The conditions defined in the way of preparing the antimisting additive E, i.e., the nature of the reaction (dehydrocondensation reaction) and the requirement to operate with a ratio [number of reactive ≡SiOH units]:[number of reactive ≡SiH units]≠1:1, allows an additive to be obtained in a liquid form which exhibits entirely remarkable antimisting properties. Without wishing to be tied to any one scientific theory or any one mechanism, it appears that this property of the antimisting additive E according to the invention is due to the selection of this ratio and to the nature of the reaction involved (dehydrocondensation reaction), which make it possible to obtain branched polymers having viscoelastic properties which are useful for controlling misting in a roll coating system operating at high speed. The rheological behavior of the antimisting additive E according to the invention may also be illustrated by the value of its elastic (G′) and viscous (G″) moduli. The antimisting additive E according to the invention:
a) is in a liquid form, optionally after dilution with a diluent J′ or a solvent J″, and
b) the tangent of the loss angle δ (tan δ) of said antimisting additive E, which is the ratio of the viscous modulus (G″) to the elastic modulus (G′), is >than 1.
The antimisting additive E according to the invention is employed in amounts which are sufficient to reduce the quantity of misting during coating. A skilled worker is of course able, by means of routine tests, to determine these amounts without difficulty. For example, he or she is able to employ the additive according to the invention in amounts of between 0.1 to 15 parts by weight relative to the total weight of the liquid silicone composition X which is a precursor of silicone coating(s).
“Dehydrocondensation” is a reaction between ≡SiH units and, on the other hand, ≡SiOH units, leading to the formation of ≡Si—O—Si≡ bonds and to the release of gaseous hydrogen. This reaction is catalyzed by an effective amount of a dehydrocondensation catalyst H.
A skilled person will know to determine the effective amount of the dehydrocondensation catalyst H in accordance with the type of catalyst used.
An effective amount for the purposes of the invention is the amount sufficient to initiate the reaction. This amount must be as low as possible, in order to allow an optimum shelf life of the composition. Useful concentrations of the catalyst are between 1·10−6 and 5, preferably between 1·10−6 and 1·10−2, parts by weight of the organosiloxane polymer solids to be reacted.
Any catalyst capable of initiating a dehydrocondensation reaction will be suitable. Metal catalysts based on platinum, rhodium, palladium, ruthenium, boron, tin or iridium, the platinum catalysts being the most common (FR-B-1 209 131, U.S. Pat. No. 4,262,107, EP-A-1 167 424, FR-A-2 806 930).
For example, it is possible to use a rhodium complex (RhCl3[(C8H17)2S]3) cited in the U.S. Pat. No. 4,262,107, a platinum complex such as the Karstedt catalyst, and metal catalysts based on platinum, rhodium, palladium, tin or iridium. Iridium-based catalysts include the following compounds: IrCl(CO)(TPP)2, Ir(CO)2(acac); IrH(Cl)2(TPP)3; [IrCl (cyclooctene)2]2 IrI(CO)(TPP)2 and IrH(CO)(TPP)3, TPP in these formulae signifying a triphenylphosphine group, and acac an acetylacetonate group.
It is also possible to use catalysts such as dibutyltin dilaurate or those cited in the Noll work “Chemistry and technology of silicones”, pages 205 and 307, Academic Press, 1968-2nd edition). Other catalysts such as boron derivatives of tris(pentafluorophenyl)borane type are described in French patent application FR-A-2 806 930. FR-B-1 209 131 discloses in particular a catalyst based on chloroplatinic acid (H2PtCl6.6H2O).
The crosslinking inhibitor D is generally used in order to endow the ready-to-use composition with a certain pot life. By varying on the one hand the nature of the catalytic entity and its concentration in the composition (giving rise to a given crosslinking rate) and on the other hand on the nature of the retardant and its concentration, it is possible to adjust the pot life. The activity of the catalytic entity is released by heating (thermal activation). The retardant is preferably selected from acetylenic alcohols (ethynylcyclohexanol: ECH) and/or diallyl maleates and/or triallyl isocyanurates and/or dialkyl maleates (diethyl maleates and/or dialkyl alkynyldicarboxylates) (diethyl acetylenedicarboxylate) or else from polyorganosiloxanes, which advantageously are cyclic and substituted by at least one alkenyl, with tetramethylvinylcyclo-tetrasiloxane being particularly preferred, or alkyl-containing maleates.
Acetylenic alcohols (see, for example, FR-B-1 528 464 and FR-A-2 372 874) are retardants which are useful according to the invention. Examples include the following:
These α-acetylenic alcohols are commercial products.
Other examples of retardants useful according to the invention include phosphine derivatives, for example tris(2,4-di-tert-butylphenyl) phosphite (sold by Ciba under the name Irgafos 168®), or those described in international patent application WO 2004/061003, and in particular the compound Irgafos® P-EPQ of formula:
A retardant of this kind is present in particular at 1-100 molar equivalents/metal of the catalyst system.
The crosslinking inhibitors I and I′ envisaged for the method according to the invention are, for example, those described for the inhibitor D. Preferably I′ is tris(2,4-di-tert-butylphenyl) phosphite (sold by Ciba under the name of Irgafos 168®).
In the liquid silicone composition X which is a precursor of silicone coating(s), it may be advantageous to employ at least one adhesion modulator system K, in order to allow control over the release properties of the crosslinked silicone coating.
As an illustration of adhesion modulator systems in silicone formulations for release on paper or adhesive tape having a polymeric carrier, mention may be made of European patent application EP-A-0 601 938, the content of which is included in its entirety in the present specification.
According to one version the adhesion modulator system K is:
Examples of diluent and/or solvent J, J′ and J″ include aliphatic and aromatic solvents and chlorinated solvents, examples being white spirit, ketones such as methyl ethyl ketone and acetone, alcohols such as isopropanol and n-butyl alcohol, saturated, unsaturated or aromatic hydrocarbons, advantageously pentane, hexane, heptane, octane, toluene, xylene, and benzene, and “naphtha” petroleum cuts; C7-C8 petroleum cuts, halogenated hydrocarbons, and mixtures thereof.
The polyorganosiloxanes A of the liquid silicone composition X which is a precursor of silicone coating(s) may be of the type which crosslink at ambient temperature or in response to heat by polyaddition reactions in the presence of a metal catalyst, in this case a platinum-based catalyst. These are crosslinkable polyorganosiloxane compositions referred to as RTV (room temperature vulcanizing) or polyaddition polyorganosiloxane compositions called HTV, which is the abbreviation of “high-temperature vulcanizable”.
The two-component or one-component RTV or polyaddition HTV polyorganosiloxane compositions cure or crosslink essentially by reaction of hydrosilyl groups with silyl alkenyl groups, generally in the presence of a metal catalyst (preferably a platinum catalyst). They 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.
The polyorganosiloxanes A may also be a type which crosslink at ambient temperature by polycondensation reactions under the action of moisture, generally in the presence of a metal catalyst, a tin compound for example (polycondensation RTV). The compositions which employ this type of polyorganosiloxane 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 (one-component compositions) and in U.S. Pat. Nos. 3,678,002, 3,888,815, 3,933,729, and 4,064,096 (two-component compositions).
The polyorganosiloxanes A which are part of these polycondensation RTV compositions are linear, branched or crosslinked polysiloxanes which carry hydroxyl groups or hydrolysable groups, alkoxy groups for example. Such compositions may further comprise a crosslinking agent which is, in particular, a compound bearing at least three hydrolysable groups, such as a silicate, an alkyltrialkoxysilane or an aminoalkyltrialkoxysilane, for example.
The liquid silicone composition X may further comprise one or more polyorganosiloxanes A which are crosslinkable cationically or free-radically:
These polyorganosiloxanes are, for example, linear or cyclic epoxysilicones and/or vinyl ethyl silicones. Epoxy- or vinyloxy-functional polyorganosiloxanes of this kind are described in particular in patents DE-4 009 889, EP-0 396 130, EP-0 355 381, EP-0 105 341, FR-2 110 115, FR-2 526 800.
The epoxy-functional polyorganosiloxanes may be prepared by hydrosilylation reactions of oils containing ≡SiH units with epoxy-functional compounds such as 4-vinylcyclohexenone or allyl glycidyl ether. The vinyloxy-functional polyorganosiloxanes may be prepared by hydrosilylation reaction of oils containing SiH units with vinyloxy-functional compounds such as allyl vinyl ether or allylvinyloxyethoxybenzene.
According to one preferred version of the method according to the invention, the liquid silicone composition X, a precursor of silicone coating(s), which is admixed with the antimisting additive E, comprises:
According to this preferred version, the polyorganosiloxane A is of the type which crosslink by polyaddition and exhibits siloxy units of the formula (III) with optionally at least some of the other units being siloxy units of average formula (IV):
in which formulae:
Examples of polyorganosiloxanes A crosslinkable by polyaddition are dimethylvinylsilyl-terminated dimethylpolysiloxanes, trimethylsilyl-terminated methylvinyldimethylpolysiloxane copolymers, and dimethylvinylsilyl-terminated methylvinyldimethylpolysiloxane copolymers.
The crosslinking organosilicon compound B is preferably of the type which exhibits units of formula (V) with optionally at least some of the other units being units of average formula (VI):
HLcSiO(3−c)/2 (V)
LgSiO(4−g)/2 (VI)
in which:
Examples of crosslinking organosilicon compound B are, for example:
The polyaddition catalyst C1 is composed, for example, of at least one metal belonging to the platinum group. This catalyst may in particular be selected from platinum compounds and rhodium compounds. Use may be made in particular of the complexes of platinum with an organic product described in U.S. Pat. No. 3,159,601, U.S. Pat. No. 3,159,602, U.S. Pat. No. 3,220,972 and European patents EP-A-0 057 459, EP-A-0 188 978, and EP-A-0 190 530, and the complexes of platinum and vinylorganosiloxanes described in U.S. Pat. No. 3,419,593, U.S. Pat. No. 3,715,334, U.S. Pat. No. 3,377,432, and U.S. Pat. No. 3,814,730. The catalyst generally preferred is platinum. In this case the amount by weight of the polyaddition catalyst C1, calculated by weight of platinum metal, is generally between 2 and 400 ppm.
Besides these constituents, the liquid silicone composition X which is a precursor of silicone coating(s) may further comprise at least one additive which is common in silicone compositions which crosslink by polyaddition, by polycondensation, cationically or free-radically. Mention may be made, for example, of pigments, etc.
According to one advantageous embodiment of the method according to the invention, the antimisting additive E has the following features:
1) by reacting, preferably at a temperature between 0° C. and 200° C.:
According to this version the antimisting additive E is a branched polymer or a mixture comprising at least one branched polymer comprising per molecule at least one reactive ≡SiH unit.
It is very advantageous to prepare the additive with a ratio [number of reactive ≡SiOH units]:[number of reactive ≡SiH units] of between 1:3 and 1:50, and more preferably still between 1:3 and 1:15. The reason is that maintaining this ratio within these ranges allows an antimisting additive to be prepared which does not exhibit gelling problems, thereby obviating dilution with a solvent or a diluent, while having an appropriate degree of branching, which is to say that the degree of branching must not be too great but must be sufficient to obtain the additive in a liquid form while maintaining the viscoelastic properties appropriate for obtaining the antimisting effect.
The use of a platinum-based metal catalyst as dehydro-condensation catalyst H makes it possible to improve the antimisting performance of the additive thus obtained.
According to one preferred embodiment of the method according to the invention, the particularly advantageous antimisting additive E obtained according to the method of preparation described above has the average formula:
MaDbD′cTd
where:
According to one particularly advantageous version of the method, in step 1) the dehydrocondensation catalyst H is a platinum-based metal catalyst, and
2) the antimisting additive E is isolated, optionally after removal of the dehydrocondensation catalyst H and/or devolatilization and/or addition of a crosslinking inhibitor I′.
According to another version of the method according to the invention, the antimisting additive E is a branched polyorganosiloxane L or a mixture comprising at least one branched polyorganosiloxane L, said antimisting additive E containing at least one reactive ≡SiOH and/or ≡SiR unit, with R being a carbinol radical, and has the following features:
1) by reacting, preferably at a temperature between 0° C. and 200° C.:
2) by isolating the antimisting additive E, where appropriate after removal of the dehydrocondensation catalyst H and/or devolatilization and/or addition of a crosslinking inhibitor I′.
Component F is preferably an organosiloxane monomer, oligomer and/or polymer F which has per molecule at least one reactive ≡SiH unit and has the general formula:
MuDvD′wTxQyM′z
in which:
Examples of constituent F include polymethylhydrosiloxanes having trimethylsiloxy and/or hydrodimethylsiloxy end groups. Very particularly suitable for the invention, for example, are the following compounds:
where a, b, c, d, and e represent a number ranging from 0 to 500;
The compound G is preferably an organosiloxane monomer, oligomer and/or polymer G which exhibits per molecule at least one reactive ≡SiOH and/or ≡SiR unit, where R is a carbinol radical, and is selected from the group consisting of the structures of formulae (I) and (II):
(DOH)iDj(THOH)kTlQmMn (I)
Mo(DR)pDqTrQs(MR)t (II)
in which:
Very particularly suitable for the invention as component G are the compounds of formula
where 1≦f≦1200, preferably 1≦f≦500, and more preferably still 4≦f≦250.
In accordance with another of its aspects, the invention provides a branched polyorganosiloxane L′, or a mixture comprising at least one branched polyorganosiloxane L′, characterized in that:
1) by reacting, preferably at a temperature between 0° C. and 200° C.:
2) by isolating the antimisting additive E, where appropriate after removal of the dehydrocondensation catalyst H and/or devolatilization and/or addition of a crosslinking inhibitor I′.
The description of the constituents used for the preparation of the branched polyorganosiloxanes L′ and L″ is as set out for the method of the invention.
The branched polyorganosiloxane L′ obtained according to the method described above contains reactive ≡SiH functions and has the advantage of being present in a liquid form, which facilitates its use in the liquid silicone composition X which is a precursor of silicone coating(s). Moreover, the use of a platinum-based metal catalyst as dehydrocondensation catalyst H makes it possible, surprisingly, to obtain a much more effective antimisting additive.
According to one preferred version of the method of preparing the branched polyorganosiloxane L′ or the mixture comprising at least one branched polyorganosiloxane L′:
According to one advantageous embodiment the branched polyorganosiloxane L′ or mixture comprising at least one branched polyorganosiloxane L′ has the average formula:
MaDbD′cTd
where:
The invention also provides a branched polyorganosiloxane L″ or a mixture comprising at least one branched polyorganosiloxane L″, characterized in that:
1) by reacting, preferably at a temperature between 0° C. and 200° C.:
2) by isolating the antimisting additive E, where appropriate after removal of the dehydrocondensation catalyst H and/or devolatilization and/or addition of a crosslinking inhibitor I′.
The invention additionally provides a liquid silicone composition X, a precursor of silicone coating(s), comprising:
The invention lastly provides for the use of the antimisting additive E as defined above to reduce misting when coating flexible supports with a liquid silicone composition X which is a precursor of silicone coating(s).
It is therefore apparent that the invention provides an original, simple, economic, and reliable means of counteracting the production of mist when coating flexible supports (of paper, film or polymeric film, for example) in roll coating devices operating at high speed. The practical industrial consequence is that the running speeds can be further increased without incidence of this misting phenomenon, which is detrimental to the quality of coating. The means of control provided by the invention also has the not-insignificant advantage of not affecting the appearance qualities, coverage, release properties, and mechanical properties (rub-off) of the crosslinked silicone coating it is desired to obtain on at least one of the faces of the flexible support.
Furthermore, the reduction in misting significantly enhances the hygiene and safety conditions for personnel stationed around industrial devices for silicone coating on rolls operating at high speed.
The purpose of the examples below is to illustrate particular embodiments of the invention, without limiting the scope of the invention to these sole embodiments.
Under an inert atmosphere, 29.8 g of a silicone oil containing 0.0597 equivalent of ≡SiOH per 100 g, 50 g of a silicone oil containing 0.4 equivalent of ≡SiH per 100 g, 16 mg of a Karstedt Pt solution containing 10-12% Pt, and 25.3 mg of ethynylcyclohexanol (ECH) inhibitor are introduced. The mixture is heated and stirred at 120° C. for 6 h until the degree of conversion (DC) of the ≡SiOH groups is −95%. After cooling, 2.64 mg of Irgafos® 168, supplied by Ciba, are added. The branched silicone oil obtained has a viscosity of 168 mm2/s and contains 0.188 equivalent of ≡SiH/100 g [ratio SiH:SiOH=11.2:1].
Under an inert atmosphere, 436.4 g of a silicone oil containing 0.0597 equivalent of ≡SiOH per 100 g, 1020 g of toluene, and 80 mg of IrCl(CO) (PPh3)2 catalyst are introduced. At ambient temperature, 523.7 g of a silicone oil containing 0.4 equivalent of ≡SiH per 100 g are run into the mixture over 2 hours. The reaction mixture is stirred for a further 2.5 h until the DC of the ≡SiOH groups is −90%. After volatiles have been stripped off, the branched silicone oil obtained has a viscosity of 960 mm2/s and contains 0.09 equivalent of SiH per 100 g [ratio SiH:SiOH=8:1].
Under an inert atmosphere, 0.86 g of a silicone oil containing 0.455 equivalent of ≡SiOH per 100 g, 80 g of a silicone oil containing 0.052 equivalent of ≡SiH per 100 g, 16 mg of a Karstedt Pt solution containing 10-12% Pt, and 25.7 mg of (ECH) inhibitor are introduced. The mixture is heated and stirred at 120° C. for 6 h until the DC of the ≡SiOH is −85%. After cooling, 2.64 mg of Irgafos® 168 are added. The branched silicone oil obtained has a viscosity of 477 mm2/s and contains 0.045 equivalent of ≡SiH/100 g [ratio SiH:SiOH=10.6:1].
Under an inert atmosphere, 80 g of a silicone oil containing 0.014 equivalent of ≡SiOH per 100 g, 10 g of a silicone oil containing 0.4 equivalent of ≡SiH per 100 g, 18 mg of a Karstedt Pt solution containing 10-12% Pt, and 33 mg of (ECH) inhibitor are introduced. The mixture is heated and stirred at 120° C. for 6 h until the DC of the ≡SiOH is −75%. After cooling, 2.8 mg of Irgafos 168 are added. The branched silicone oil obtained has a viscosity of 31 000 mm2/s and contains 0.028 equivalent of ≡SiH/100 g [ratio SiH:SiOH=3.57:1].
Under an inert atmosphere, 10 g of xylene and 18 mg of a Karstedt Pt solution containing 10-12% Pt are introduced. The mixture is heated and stirred at 120° C. and then 65.5 g of a silicone oil containing 0.014 equivalent of ≡SiOH per 100 g and 24.4 g of a silicone oil containing 0.4 equivalent of SiH per 100 g are run together into the mixture over 3 hours. The reaction mixture is heated for a further 3 h at 120° C. until the DC of the ≡SiOH is −86%. After volatiles have been stripped off, the branched silicone oil obtained has a viscosity of 11 600 mm2/s and contains 0.087 equivalent of ≡SiH per 100 g [ratio SiH:SiOH=10.63:1]. The empirical formula of the product is determined by 29Si and 1H NMR is MD52D′3.4T0.6M.
For comparison, a branched silicone with empirical formula similar to that of example 5 was prepared by redistribution of 9.2 g of a resin of formula M0.7D1.2T3.3, 164.4 g of cyclic polysiloxane of formula D4 (octamethylcyclotetrasiloxane), 16.6 g of a silicone oil of formula M2D4 (tetradecamethylhexasiloxane), and 9.8 g of a polysiloxane with ≡SiH unit, of formula MD′50M, in the presence of Tonsil (montmorillonite sold by Süd-Chemie] at 75° C. for 20 h. Following filtration and removal of the volatiles by stripping, the branched silicone product obtained has a viscosity of 135 mm2/s. The empirical formula of the product, as determined by 29Si and 1H NMR, is MD67D′3.6T0.5M. It should be noted that the empirical formula of this polymer is very close to that described for the polymer of example 5.
Under an inert atmosphere, 28.1 g of a silicone oil containing 0.014 equivalent of ≡SiOH and 26.3 mg of a Karstedt Pt solution containing 10-12% Pt are introduced. The mixture is heated and stirred at 100° C. and then 33.3 g of a silicone oil containing 0.4 equivalent of ≡SiH per 100 g and 78.8 g of the silicone oil containing 0.014 equivalent of ≡SiOH are run in simultaneously over 2 hours. The reaction mixture is subsequently heated at 100° C. for a further 2 h. The mixture is cooled to 85° C. and then 49 g of tetradecene are added. The mixture is heated at 85° C. for 3 h and then cooled. After volatiles have been stripped off, the branched silicone oil obtained has a viscosity of 2730 mm2/s and contains 0.4 milliequivalent of ≡SiH per 100 g.
Under an inert atmosphere, 160.15 g of a silicone oil containing 0.014 equivalent of ≡SiOH, 300 mg of a Karstedt Pt solution containing 10-12% Pt, and 20 g of a silicone oil containing 0.4 equivalent of ≡SiH per 100 g are introduced. The mixture is heated and stirred at 110° C. for 1.5 h, but leads to the formation of a gel, which means that it cannot be used as it is and requires dilution with a diluent or solvent.
Measurement of the parameter of tangent of the loss angle δ (tan δ)=the ratio of the viscous modulus (G″) to the elastic modulus (G′):
The viscoelasticity was measured at different frequencies for two examples, using a rheometer as follows: Rheometric ARES/diameter: 50 mm/cone angle/angle: 0.04 rad/cone-plane spacing: 53 μm.
The results obtained are collated in the table below.
Branched silicones prepared in section I) were tested as antimisting additives. The results observed are collated in the tables below, as a measured misting quantity (mg/m3) or in the form of a ratio of misting measured with additive and without additive for different roll rotation speeds.
To analyze and quantify the mist produced in a roll coating device operating at high speed, use was made on the laboratory scale of a 2-roll device (provided by Ermap, Grenoble, France) operating reproducibly and capable of conveying a web of paper at a linear speed of more than 900 m/min. The two press/coating rolls have a diameter of 10 cm. The press roll is covered with rubber and the coating roll with chromium. The coating roll was cut in dumbbell shape so that the speed of the two rolls is synchronous. The press roll, which can be driven by a motor, is in constant pressure contact with the coating roll. The silicone coating liquid is poured directly into the nip between the two rolls. The amount of fluid used is 0.25 ml.
Different compositions were then prepared by mixing a silicone polymer A1 (a polydimethylsiloxane whose end groups are blocked with a dimethylvinylsiloxy group, and whose viscosity is 220 mPa·s) and the products described above in examples 4 to 7, at a rate of 2 parts by weight of product in 100 parts by weight of polymer. The compositions are homogenized on a barrel rolling device for the time required. Then the rotary system described above is used on the rolls on which the preparation in question is spread. Subsequently the rotational speed of the rolls is progressively increased. In parallel, the density of the mist is measured by placing a measurement instrument referred to as a particle counter, which is sold by ITS (France), in proximity to the point of contact between the rolls. The result of the mist density measurement is expressed in mg of silicone aerosol per m3 of air at a given measurement speed.
The table below collates the results obtained:
These results show that a branched polymer according to the invention prepared with a Pt-based dehydrogenation catalyst (examples 4, 5, and 7) exhibits an activity which is 3 to 9 times greater than that of a branched polymer according to the invention prepared from an iridium-based dehydrogenation catalyst (example 2).
Moreover, a comparison of example 5 (inventive) and example 6 (comparative) shows that a branched polymer obtained by a dehydrocondensation reaction exhibits an antimisting activity which is greatly superior to that of a branched polymer obtained by another synthesis route.
Baths are obtained by mixing the following products in succession:
The proportions of the mixture are calculated such as to give, in the final bath, a ratio between the total number of moles of vinyl groups and the total number of moles of hydrosiloxane groups of 1.75, a platinum concentration of 110 ppm, and an ethynylcyclohexan-1-ol content of the order of 0.15% by weight relative to the weight of the formulation. Furthermore, the antimisting additive according to the invention is added to the polydimethylsiloxane silicone polymer whose ends are blocked with a dimethylvinylsiloxy group and whose viscosity is 220 mPa·s in a proportion of 2% by weight relative to the total weight of the formulation. These baths are then used in succession to coat a “glassine” paper support by means of a coating machine whose coating head is a head fitted with four wet rolls. Downstream of this head, a drying station in which air circulates at approximately 195° C. is used in order to cure the silicone coating by taking it to a maximum temperature of between 130 and 160° C.
After having carried out coating by using the above-described baths in succession, results are obtained which are comparable in terms of the reduction in mist during coating, the coating obtained being dry to the touch and of release character.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0512508 | Dec 2005 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/069408 | 12/7/2006 | WO | 00 | 1/23/2009 |
