Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
  • C09D183/04—Polysiloxanes

Definitions

• the invention relates to the general field of silicone coating on high-speed cylinders of various flexible supports, such as sheets of paper or of synthetic polymer (polyolefin, polyester, etc.), or even of textile.
• the invention relates to the coating of flexible materials with liquid compositions containing one or more polyorganosiloxanes (POS) crosslinkable by polyaddition, by polycondensation (in emulsion), by cationic route or by radical route, so as to form a film. or protective coating having in particular non-stick and / or hydrophobic properties.
• POS polyorganosiloxanes
• the flexible supports can be papers, cardboards, plastic films, or metallic films.
• the applications of these silicone coated supports are for example: food paper (baking molds, packaging), label / adhesive tape, seal, etc.
• the coating of these flexible supports with crosslinkable liquid silicones is carried out on coating devices operating continuously, and at very high speed.
• These devices include coating heads made up of several cylinders including in particular a pressure cylinder and a coating cylinder, which is continuously supplied with crosslinkable liquid silicone composition, by means of a series of cylinders joined to each other.
• the flexible support strip circulates at high speed between the pressure cylinder and the coating cylinder to be coated on at least one of its faces with a silicone film intended to crosslink by means of crosslinking means arranged downstream of the head. coating.
• These crosslinking means can be emitters of heat, radiation (egUV) or electron beams for example.
• mist or an aerosol are reflected in particular by the appearance of a mist or an aerosol ("misting", “fogging") in the environment of the coating head and, more particularly, at the level of the contacts between the cylinders in rotation and / or between the coating cylinder and the flexible support to be coated.
• the density of this mist or of this aerosol increases when the linear speed of travel and therefore the speed of rotation of the cylinders increases.
• C. increase in the difference between the tangential speed of the coating cylinder and the linear speed of the paper. But beyond a certain differential, the homogeneity of the coated layer is seriously disturbed. In addition, this makes it possible to reduce the density of the mist without destroying it sufficiently to allow a significant increase in the coating speed; D. increase in pressure between the coating cylinder and the pressure cylinder; here again within a certain limit and without interesting suppression of the phenomenon of formation of fog.
• Another approach for combating the formation of fog in roller coating machines consists in acting on the formulation of the liquid silicone coating composition. According to this approach, it is known to reduce the average degree of polymerization in number of POSs constituting the silicone coating liquid and, consequently, to reduce the viscosity of the silicone coating bath to limit the density of the mist. These known methods suffer from a serious drawback which is to modify the properties appreciably and, in particular, the anti- adhesion of the flexible silicone support that is sought.
• EP-0 716 115 describes a process for manufacturing a silicone composition for coating at high speed with cylinders, this composition being presented as allowing the reduction of the density of fog.
• a polydimethylmethylhydrogenosiloxane with trimethylsilyl ends of degree of polymerization equal to 12 is used, as well as 0.01% of a polydimethylsiloxane substituted by perfluoethylbutyl and ethylvinyl functions, the ends of which are of the dimethylvinylsiloxyl type.
• the functionalization patterns can be hydrophobic residues such as stearic or oleic acid residues.
• compositions are relatively complex and therefore expensive to obtain. Furthermore, they still need to be improved as regards the fight against the formation of mist in the silicone coating on cylinders, at high speed.
• liquid coating compositions also comprise a platinum-based catalyst and a rheological additive consisting of silica with a high specific surface, in particular combustion silica, in an amount of less than 1% and less than 5%. dry weight, in Examples XII and XIII respectively.
• This composition also comprises a polymethylhydrogenosiloxane capable of reacting with POS Si-Vi in the presence of a platinum catalyst.
• compositions intended to be coated on flexible supports to form, after crosslinking by the cationic route under UV, a non-stick coating.
• these compositions comprise cellulose fibers having an average length of between 15 and 100 ⁇ m and an average thickness of between 5 and 40 ⁇ m.
• the POSs implemented are POSs functionalized by groups of crosslinking of the acryloxy or methacryloxy type, allowing crosslinking by radical route under UV.
• the cellulose fibers incorporated into the composition make it possible to provide a solution to the technical problem which is to obtain a non-brittle crosslinked non-stick silicone coating.
• Cellulose fibers are presented as providing improvements with regard to the transfer of the coating silicone film onto the support, the cutting resistance, the mechanical properties (tensile and tear resistance), the fixing of the coating. on paper, the reduction in the absorption of coating liquid within the paper, and incidentally the reduction in the formation of mist.
• US Pat. No. 6,057,033 does not provide any quantitative element for assessing the reduction in fog caused by cellulosic fibers. There is every reason to believe that this reduction remains entirely insufficient.
• particulate fillers for example siliceous fillers
• liquid silicone compositions intended to be coated on flexible supports for example made of paper to form crosslinked non-stick coatings
• the Japanese patent application JP-62 64 011 which describes a coating liquid containing a film-forming resin and a solvent and which also contains wax particles with a diameter between 1 and 10 ⁇ m, the diameter of the particle, will also be cited for the record. the largest being at most equal to 150% of the thickness of the wet coating film applied to the support.
• Such a coating liquid would allow an increase in the coating speed of at least 10 to 30 m / min, a priori thanks to a limitation of the formation of fog.
• one of the essential objectives of the invention is to propose an effective method of combating the appearance of mist when coating flexible supports with a liquid silicone composition precursor of crosslinked coatings, this coating being effected using a cylinder coating device operating at high speed.
• Another essential objective of the invention is to propose an economical and simple method of combating the appearance of mist when coating flexible supports with a silicone composition intended to crosslink, this coating operating in a device for high speed roller coating.
• Another essential objective of the invention is to propose a process for coating flexible supports at high speed on a cylinder device, in which the formation of mist is reduced, so that the speed of appearance of this disturbance is significantly increased.
• Another essential objective of the invention is to provide a new additive making it possible to reduce the formation of mist when coating at high speed on cylinders, flexible materials, by means of silicone compositions crosslinkable in non-stick coatings.
• Another essential objective of the invention is to propose a method of combating the appearance of mist in the context of the coating of flexible supports, with a crosslinkable silicone composition in non-stick coatings, using a cylinder coating device, said method having to have positive effects on the appearance and / or the covering and / or the mechanical properties (rub-off) and / or the anti-adhesion properties of the crosslinked coating which it is sought to obtain on at least one of the faces of the flexible support.
• liquid precursor of silicone coating (s), using a roller coating device the liquid composition comprising:
• -A- at least one polyorganosiloxane (POS) crosslinkable by polyaddition, by polycondensation, by cationic route or by radical route;
• -B- optionally at least one crosslinking organosilicon compound;
• -C- optionally at least one catalyst for the crosslinking reaction; characterized in that a liquid coating composition obtained by mixing: • a silicone phase comprising one or more POSs is used
• the result obtained thanks to the invention is an effective control of the formation of mist, which results in a significant increase in the speed of appearance of said mist in a cylinder coating system operating at high speed.
• the amount of water present in the composition is controlled by: - the ESAAB concentration in the composition, - and the proportion of ⁇ a in the ESAAB.
• the particle size is likely to decrease.
• ESAAB is a direct oil-in-water emulsion
• a multiple oil-in-water-in-oil emulsion is formed in situ.
• the particle size of the dispersed phase ⁇ d of the ESAAB is chosen so as to confer a certain stability on the ESAAB. This particle size is not critical. However, to fix the ideas, it will be specified that the dispersed phase ⁇ d of the ESAAB is formed by droplets whose particle size, given by their D 50 (in ⁇ m), is such that:
• the parameter D 50 is the median size of the particle size distribution. It can be determined on the cumulative particle size distribution graph, obtained by one of the analytical techniques mentioned below, by determining the size corresponding to the cumulative 50% of the population of particles. Concretely, this particle size parameter D 50 corresponds to the maximum average dimension of at least 50% of the mass of particles considered, a D 50 of 10 ⁇ m indicates that 50% of the particles have a size less than 10 ⁇ m.
• Granulometry measurements can be carried out by conventional techniques such as sedimentation, laser diffraction (for example COULT ⁇ R® LSI30), optical microscopy coupled with image analysis, etc.
• 1 ESAAB is a reverse emulsion of the water in oil type.
• This inverse ESAAB of the water-in-oil type is an emulsion: - whose dispersed phase ⁇ d is formed by droplets of water optionally additive, the D so of these droplets being as defined above,
• ESAAB is a direct emulsion of the oil-in-water type.
• This direct oil-in-water ESAAB is an emulsion:
• ESAABs reverse or direct ESAABs are obtained by emulsification methods well known to those skilled in the art. These methods involve the mixing of an aqueous phase and an oily phase without and with grinding, that is to say under high shear.
• the inversion emulsification processes for obtaining, for example, oil-in-water emulsions involve the prior formation of a water-in-oil emulsion (commonly known as a reverse emulsion) and then the inversion of this emulsion, whereby obtains an emulsion in water.
• a water-in-oil emulsion commonly known as a reverse emulsion
• the direct emulsification processes for obtaining emulsions of oil-in-water or water-in-oil type are processes in which the emulsion is throughout its entire duration. preparation and as soon as it is formed, a direct emulsion, that is to say an oil-in-water or reverse water-in-oil emulsion.
• ESAAB emulsions are advantageously stabilized using one or more surfactants.
• These surfactants can be non-ionic, anionic, cationic, or even zwitterionic.
• the surfactants are chosen more generally as a function of the HLB.
• HLB Hydrophilic Lipophilic Balance
• HLB values are notably reported in various basic manuals such as the "Handbook of pharmaceutical excipients, The Pharmaceutical Press, London, (1994)".
• the stabilization of the silicone / water emulsions can be carried out using protective colloids such as polyvinyl alcohols.
• Water / silicone emulsions can also be stabilized using polyether silicones [Surfactant silicone - Surfactant Science series V86 Ed Randal M. Hill (1999)].
• solid particles can allow the stabilization of oil-in-water or water-in-oil emulsions.
• silica particles - preferably hydrophilic - whose contact angle is close to 0 °, as a means of stabilizing the ESAAB ( water-in-oil or oil-in-water emulsion), in combination with at least one adequate co-stabilizer.
• the role of the latter is to allow the modification of the contact angle.
• the co-stabilizers can be nonionic, anionic, cationic or even zwitterionic surfactants.
• specific treatments of particulate hydrophilic silica make it possible to obtain variable degrees of hydrophobization and to optimize the contact angle.
• the formation of an oil-in-water emulsion is favored when the contact angle between the oil, the solid and the water is less than 90 ° C.
• the contact angle is greater than 90 ° C, a water-in-oil emulsion can be stabilized.
• the invention also relates to a means for stabilizing aqueous silicone emulsions, comprising silica particles - preferably hydrophilic - associated with at least one co-stabilizer, preferably chosen from those mentioned above.
• 1 ESAAB is implemented with non-cellulosic anti-fog particles whose particle size given by their D 50 (in ⁇ m) is such that:
• these anti-fog particles are selected from the group comprising:
• the specific surface of these BET anti-fog particles is between 0.5 m 2 / g and 500 m 2 / g, preferably between 2 and 400 m 2 / g, and more preferably between 5 and 300 m 2 / g.
• the anti-fog particles consist of silica
• it may be colloidal silica, precipitation silica or pyrogenic silica.
• silicas are preferably used as they are or may alternatively, have undergone a surface treatment using organosilicon compounds usually used for this use.
• organosilicon compounds usually used for this use.
• these compounds are: A. methylpolysiloxanes such as hexamethyldisiloxane, octamethylcyclotetrasiloxane,
• methylpolysilazanes such as hexamethyldisilazane, hexamethyltrisilazane,
• chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane,
• D. alkoxysilanes such as dimethyldimethoxy-silane, dimethylvinylethoxysilane, trimethyl-methoxysilane, octyltriethoxysilane.
• the silicas can increase their starting weight up to a rate of 20%, preferably around 18%.
• the anti-fog particles based on synthetic polymers consist of polymers resulting from a conventional emulsion copolymerization process of one or more polymerizable organic monomers. These organic monomers are preferably chosen from:
• the alkyl (meth) acrylates the alkyl part of which preferably contains from 1 to 18 carbon atoms, in particular methyl acrylate, ethyl acrylate, propyl acrylate, acrylate of n-butyl, isobutyl acrylate, amyl acrylate, lauryl acrylate, isolamyl acrylate, (2 ethyl-2 hexyl) acrylate, octyl acrylate , methyl methacrylate, chloroethyl methacrylate, butyl methacrylate, (3, 3 butyl dimethyl) methacrylate, ethyl methacrylate, isobutyl methacrylate, isopropyl methacrylate, phenyl methacrylate , butyl chloroacrylate, methyl chloroacrylate, ethyl chloroacrylate, isopropyl chloroacrylate, cyclohex le chloroacrylate;
• vinyl aromatics preferably having at most 24 carbon atoms and chosen in particular from styrene, 1 ⁇ -methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methoxystyrene, 2-hydroxymethylstyrene, 4-ethylstyrene, 4-ethoxystyrene, 3, 4-dimethylstyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chloro-3-methylstyrene, 4-tert-butylstryrene, 4 - dichlorostyrene, 2, 6-dichlorostyrene, 2,5-difluorostyrene, and 1-vinylnaphthalene;
• conjugated aliphatic dienes preferably having from 3 to 12 carbon atoms, in particular 1,3-butadiene, isoprene and 2-chloro-1,3-butadiene;
• nitriles preferably having from 3 to 6 carbon atoms such as acrylonitrile and methacrylonitrile.
• PAB all other polymers - with the exception of cellulosic polymers - which are preferably in the form of powders obtained by processes known per se, for example: cryogenic grinding, prilling, atomization ...
• These polymer powders can be, for example, powders of polyamides, of polytetrafluoroethylene (PTFE).
• the mode of preparation of the liquid coating composition comprising at least one ESAAB, or even charged with anti-fog particles, also constitutes one of the essential elements of the present invention.
• the silicone phase it is preferable to mix at least part of the silicone phase with all or part of the ESAAB, or even anti-fog particles in dry powder form and / or in the form of a suspension in a liquid (organic or aqueous), preferably in powdery dry form.
• this intermediate mixture then being mixed with the silicone phase, in continuous or dispersed form, comprising the residual fraction of the silicone phase.
• the ESAAB silicone phase mixture or even anti-fog particles is carried out using a conventional mixer, known to be dispersant in fluid media by operating at room temperature.
• slow dispersers By way of examples, mention may be made of slow dispersers, static mixers, paddle mixers, single or multiple screw extruders, planetary mixers, hook mixers, slow dispersers.
• liquid silicone composition may comprise other additives initially contained in the silicone phase or incorporated during mixing with the ESAAB, or even the anti-fog particles.
• the following products are chosen as constituents of the silicone phase of the liquid coating composition:
• W is an alkenyl group, preferably vinyl or alkyl
• - Z is a monovalent hydrocarbon group, free from any adverse action on the activity of the catalyst and preferably chosen from alkyl groups having from 1 to 8 carbon atoms included, advantageously, from methyl, ethyl, propyl and 3, 3, 3-trifluoropropyl and also among the aryl groups and, advantageously, among the xylyl and tolyl and phenyl radicals,
• Z has the same meaning as above and c has a value between 0 and 3, for example between 1 and 3; dimethylpolysiloxanes with dimethylvinylsilyl ends, methylvinyldimethylpolysiloxane copolymers with trimethylsilyl ends, methylvinyldimethyl- polysiloxane copolymers with dimethylvinylsilyl ends, cyclic methyl vinylpolysiloxanes, being more specially selected;
• - L is a monovalent hydrocarbon group, free from any unfavorable action on the activity of the catalyst e chosen, preferably, from alkyl groups having from 1 to 8 carbon atoms included and, advantageously, from the methyl, ethyl, propyl and 3, 3, 3-trifluoropropyl groups and also from the aryl groups and, advantageously, from the xylyl and tolyl and phenyl radicals,
• - d is 1 or 2
• c is 0, 1 or 2
• d + c has a value 'between 1 and 3
• L has the same meaning as above and g has a value between 0 and 3, and the poly (dimethylsiloxane) (methylhydrogenosiloxy) ( ⁇ , ⁇ -dimethylhydrogeno) siloxane, being more specially selected.
• POSs can be of the type which crosslink at room temperature or with heat by polyaddition reactions in the presence of a metal catalyst, in this case based on platinum.
• RTV Room Temperature Vulcanizing
• EVC polyaddition POS compositions called EVC which is the abbreviation for "hot vulcanizable elastomer”.
• POS compositions RTV or EVC of polyaddition essentially by reaction of hydrogenosylyl groups on alkenyl sylyl groups, in the general presence of a metal catalyst (preferably platinum), are described for example in US Patents 3,220 972, 3,284,406, 3,436,366, 3,697,473 and 4,340,709.
• the liquid silicone composition used can be chosen from two-component or single-component POS compositions which crosslink at room temperature by polycondensation reactions under the action of humidity, generally in the presence of a metal catalyst, for example a tin compound (RTV polycondensation).
• a metal catalyst for example a tin compound (RTV polycondensation).
• the POSs entering into these polycondensation RTV compositions are branched or crosslinked linear polysiloxanes carrying hydroxyl groups or hydrolysable groups, for example alkoxy.
• Such compositions may 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 aminoalkyl trialkoxysilane.
• the liquid silicone coating composition can also comprise one or more crosslinkable POSs by cationic or radical route: - in the presence of an effective amount of cationic initiator systems (thermal initiators and / or photoinitiators) - initiators of the onium borate type or organometallic complexes, organic solvents which donate protons (isopropyl alcohol, benzyl alcohol ... - and / or as the case may be in the presence of a radical initiator, via activation by actinic radiation (UV ) or by electron beams.
• POSs are, for example epoxysilicones and / or vinylethersilicones, linear or cyclic.
• epoxy or vinyloxyfunctional POSs 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 functional epoxy POSs can be prepared by hydrosylylation reactions between oils with SiH units and epoxy compounds -functional such as vinyl-4-cyclohexenone or allyl-glycidyl ether.
• the vinyloxyfunctional POSs can be prepared by hydrosilylation reaction between oils with SiH units and vinyloxyfunctional compounds such as allylvinylether or allylvinyloxyethoxybenzene.
• liquid silicone coating composition may also contain:
• additives (F) there may be mentioned:
• retarders of the addition reaction e.g. tetramethylvinyltetrasiloxane, pyridine, phosphines, phosphites, unsaturated amides and acetylenic alcohols;
• crosslinking agents such as alkyltrialkoxysilane, alkyl silicates, alkyl polysilicates (methyl, ethyl silicate, isopropyl silicate, n-propyl silicate, etc.) ;
• pigments of the carbon black type titanium dioxide, phthalocyanine, benzimidazolone, naphthone, diazopyrazolone ...,. photosensitizers chosen from products (poly (aromatics) - possibly metallic - and heterocyclic products (phenotiazine, tetracene, perilene, anthracene, xantopinacole, thioxantone ...);
• the liquid silicone coating composition is a silicone oil:
• diluent and / or solvent (Di) which comprises one or more POS (A), optionally a compound (B) - and optionally a diluent and / or a solvent (Di) -, - and which is loaded with ESAAB, or even with anti-fog particles.
• diluent and / or solvent (Di) mention may be made of aliphatic and aromatic solvents, chlorinated solvents, e. g.
• the liquid silicone coating composition is an aqueous emulsion of silicone phase based on compounds (A) and (B), and optionally charged with anti-fogging particles.
• silicone emulsions are obtained in a manner known per se, for example as described in French patent application No. 97 16872, the content of which is incorporated into the present description by reference.
• the invention relates to the use of ESAAB (or even non-cellulosic particles) as anti-fog additives in crosslinkable liquid silicone compositions intended for coating flexible supports to form crosslinked coatings , with the aid of roller coating device, so as to combat the appearance of fog during coating, characterized in that 1 ESAAB (or even anti-fog particles) are as defined above.
• the invention also relates to a method of coating flexible supports with at least one liquid silicone composition precursor of silicone coating (s), this coating being effected using a roller coating device, characterized in that use is made of the method of combating the appearance of mist ("misting") as defined above.
• the invention provides an original simple, economical and reliable means of combating the production of mist when coating flexible supports (for example paper, film or polymer film) with a crosslinkable liquid silicone composition. , in cylinder coating devices operating at high speed.
• the practical industrial consequence is that the running speeds can be further increased without the appearance of this phenomenon of fog detrimental to the quality of the coating.
• the control means proposed by the invention also has the non-negligible advantage of not adversely affecting the appearance qualities, the coverage, the anti-adhesion properties, as well as the mechanical properties (rub-off) of the coating crosslinked silicone that is sought to be obtained on at least one of the faces of the flexible support.
• the viscosity is measured using a BROOKFIELD viscometer according to the indications of standard AFNOR NFT 76 106 of May 1982.
• ESAAB Anti-Fog Silicone Emulsions
• Trideceth.8 is a surfactant consisting of an ethoxylated alcohol.
• PI polymer polydimethylsiloxane, the ends of which are blocked by a dimethylvinylsiloxy group and whose viscosity is approximately 600 mPa.s,
• polymer P2 polydimethylsiloxane the ends of which are blocked by a dimethylvinylsiloxy group and the viscosity of which is approximately 200 mPa.s,
• a laboratory scale was used device with 2 rollers operating in a reproducible manner and able to run a strip of paper at a line speed of more than 900m / min.
• a sufficiently powerful light projector was installed so as to illuminate all of the 2 presser / coater cylinders and to be able to observe from what speed the cylinders rotate the fog becomes visually detectable.
• the two pressure / coating rollers have a diameter of 10 cm.
• the pressure cylinder is covered with rubber and the chrome coating cylinder.
• the coating cylinder was cut in a dumbbell so that the speed of the two cylinders were synchronous.
• the pressure cylinder driven by a motor is in constant pressure contact with the coating cylinder.
• the silicone coating liquid is poured directly into the burial between the two rollers.
• the amount of fluid used is 1 ml or 0.25 ml.
• compositions were then prepared by mixing a silicone polymer (PI, P2, P3 as defined above) and various direct or reverse emulsions.

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