MX2008009112A - Insulated glass unit with sealant composition having reduced permeability to gas - Google Patents

Abstract

The invention relates to a high thermal efficiency, insulated glass unit structure sealed with a cured composition containing, inter alia, diorganopolysiloxane(s) and inorganic-organic nanocomposite(s), the cured composition exhibiting low permeability to gas(es).

Description

ISOLATED GLASS UNIT WITH SEAL COMPOSITION THAT HAS REDUCED PERMEABILITY TO GAS FIELD OF THE INVENTION This invention relates generally to thermally insulating structures, and more particularly to an insulated glass unit structure, of high thermal efficiency, sealed with a composition cured at room temperature that exhibits low permeability to glass or gas mixtures.

BACKGROUND OF THE INVENTION [0002] Insulating glass units (GUs) commonly have two glass panels separated by a separator. The two glass panels are placed parallel to each other and sealed at their periphery so that the space between the panels, or the internal space, is completely enclosed. The internal space is normally filled with air. The energy transfer through an insulating glass unit of this typical construction is reduced, due to the inclusion of the insulating layer of air in the internal space, compared to a single glass panel. The energy transfer can also be reduced by increasing the separation between the panels to increase the air insulating blanket. This is a limit for the maximum separation beyond which the convection within the air between the panels can increase the transfer of energy. The energy transfer can be further reduced by adding more layers of insulation in the form of additional internal spaces and closing the glass panels. For example, three parallel separated glass panels separated by two internal spaces and sealed in their periphery. In this way the separation of the panels is kept below the maximum limit imposed by the effects of convection in the air space, even the global energy transfer can be reduced further. If additional reduction in energy transfer is desired then additional internal spaces can be added. Additionally, the energy transfer of sealed insulating glass units can be reduced by replacing the air in a sealed insulated glass window for a denser gas of lower conductivity. Suitable gases should be colorless, non-toxic, non-corrosive, non-flammable, unaffected by exposure to ultraviolet radiation and more dense than air, and of conductivity lower than air. Argon, krypton, xenon and sulfur hexafluoride are examples of gases that are commonly replaced by air in insulating glass windows to reduce energy transfer.

Various types of sealants are currently used in the manufacture of insulated glass units including curing and non-curing systems. Liquid polysulphides, polyurethanes and silicones represent healing systems, which are commonly used, while polybutylene-polyisoprene copolymer rubber based on hot melt sealants commonly use non-curing systems. Liquid polysulfides and polyurethanes are generally two component systems comprising a base and a curing agent that are mixed just prior to application to the glass. Silicones can be one-component as well as two-component systems. Two-component systems require a fixed mixing ratio, two-part mixing equipment and cure time before the insulating glass units are switched to the next manufacturing stage. However, current RTC silicone seal compositions, while effective to some degree, still have only a limited capacity to prevent the loss of low thermal conductivity gas, e.g., argon, from the internal space of a IGU. As a result of this permeability, the reduced energy transfer maintained by the gas between the glass panels is lost over time.

Therefore, there is a need for an IGU with a reduced gas permeability RTC composition compared to that of known PTC compositions. When used as the sealant for IGU, a reduced gas permeability RTC composition will retain the intra-panel insulating gas of an I-GU over a longer period compared to that of a more permeable PTC composition and therefore It will extend the insulating properties of IGU over a longer period of time.

SUMMARY OF THE INVENTION The present invention relates to an insulated glass unit with increased thermal insulation stability. Specifically, the present invention relates to an insulated glass unit comprising at least two separate glass sheets (panels), or another material of equivalent functionality, in separate relation to each other, a gas of low thermal conductivity between them and a gas seal assembly including a cure, that is, a curable, crosslinked or vulcanized seal composition, comprising: a) at least one diorganopolysiloxane terminated in silanol; b) at least one interlayer for the diorganopolysiloxane terminated in silanol; c) at least one catalyst for the crosslinking reaction; d) a gas barrier that increases the amount of at least one inorganic-organic nanocomposite, and optionally, e) at least one solid polymer having gas permeability that is less than the permeability of the interlaced diorganopolysiloxane. When used as a component of the IGU gas seal assembly, the above cured sealing composition reduces the gas loss of the IGU thereby extending its useful service life.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional side view of a double glazed insulated glass unit (IGU) having a gas seal assembly including a cured seal composition according to the invention. Fig. 2 is a graphical presentation of permeability data for the seal compositions of Comparative Example 1 and Examples 1 and 2. Fig. 3 is a graphical presentation of permeability data for the seal compositions of Comparative Example 2 and Example 3.

Fig. 4 is a graphical presentation of permeability data for the seal compositions of Comparative Example 3 and Examples 4 and 5.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, an insulated glass unit comprising increased thermal insulation stability is provided with at least two separate sheets of glass in separate relation therebetween, an insulating gas of low thermal conductivity or a gas mixture therebetween and a gas sealing member including a cured seal composition resulting from the curing of a curable seal composition comprising: a) at least one diorganopolysiloxane terminated in silanol; b) at least one interlayer for the diorganopolysiloxane terminated in silanol; c) at least one catalyst for the crosslinking reaction; d) an amount that increases the gas barrier of at least one inorganic-organic nanocomposite filler; and optionally, e) at least one solid polymer having a gas permeability that is less than the permeability of the interlaced diorganopolysiloxane. With reference to Fig. 1, the insulated glass unit 10 of known and conventional construction includes glass sheets 1 and 2 held in separate relation by a gas sealing assembly having a primary gas sealing member 4, the continuous separating member 5 and low gas permeable seal composition 7 prepared as described above, the space 6 between the sheets 1 and 2 being filled with an insulating gas or gases such as argon. A glazed bead 8, as is known in the art, is placed between glass sheets 1 and 2 and window frame 9. The panels 1 and 2 can be made from any of a variety of materials such as glass, e.g., transparent floating glass, annealed glass, tempered glass, solar glass, inked glass, e.g., low energy glass, etc., acrylic resin and polycarbonate resin, and the like. The inclusion of cured seal composition 7 in the above gas seal assembly provides improved gas barrier characteristics and moisture leakage characteristics in relation to known and conventional gas sealants. As a result, the cured seal composition 7 provides longer service performance of insulated glass units of all forms of construction including that specifically described above. The primary seal member 4 of the insulated glass unit may be comprised of polymeric materials known in the art, for example, rubber-based materials such as poly-isobutylene, butyl rubber, polysulfide, EPDM rubber, nitrile rubber, and the like. Other useful materials include, polyisobutylene / polyisoprene copolymers, polysiobutylene polymers, brominated olefin polymers, copolymers of polyisobutylene and para-methylstyrene, copolymers of polyisobutylene and brominated para-methylstyrene, butyl rubber copolymer of isobutylene and isoprene, ethylene-propylene polymers, polysulfide polymers, polyurethane polymers, styrene butadiene polymers and the like. As indicated above, the primary gas seal member 4 can be raged with a material such as polyisobutylene which has very good seal properties. The glazed bead 8 is a sealant that is sometimes referred to as glaze pellets and can be provided in the form of a silicone or butyl rubber. A desiccant can be included in continuous separator 5 in order to remove moisture from the space occupied by insulating gas between glass panels 1 and 2. Useful desiccants are those that do not adsorb the gas / insulating gas (s) that fill (n) the inside of the insulated glass unit. Gases of suitable low thermal conductivity and mixtures of said gases for use in the insulated glass unit are well known in include transparent gases such as air, carbon dioxide, sulfur hexafluoride, nitrogen, argon, krypton, xenon and the like and mixtures thereof.

Suitable silanol-terminated diorganopolysiloxanes (a) include those of the general formula: MzDbD'c where "a" is 2, and "b" is equal to or greater than 1 and "c" is zero or positive; M is (HO) 3_x-yR1xR2ySi01 / 2 where "x" is 0, 1 or 2 and "y" is 0 or 1, subject to the limitation that x + y is less than or equal to 2, R1 and R2 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms, D is R3R4SiO? / 2; wherein R3 and R4 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms; and D1 is R5R6Si02 2; wherein R5 and R6 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms. Suitable binders (b) for the silanol-terminated diorganopolysiloxane present in the composition of the invention include alkyl silicates of the general formula: (R140) (R150) (R170) Si wherein R14, R15, R16 and R17 are each independently a monovalent hydrocarbon group of up to 60 carbon atoms.

Interleavers of this type include n-propyl silicate, tetraethyl ortho silicate and methyltrimethoxysilane and similar alkyl-substituted alkoxysilane compounds, and the like. Suitable catalysts (c) for the crosslinking reaction of the silane-terminated diorganopolysiloxane can be any of those known to be useful in facilitating the entanglement of said siloxanes. The catalyst can be a metal-containing or non-metallic compound. Examples of compounds containing useful metals include those of tin, titanium, zirconium, lead, iron, cobalt, antimony, manganese, bismuth and zinc. In one embodiment of the present invention tin-containing compounds useful as crosslinking catalysts include dibutyltin dilaurate, dibultiltin diacetate, dibutyltin dimethoxide, tin octoate, isobutyltin triceroate, dibutyltin oxide, soluble dibutyltin oxide, bis-di dibutyltin isobutylphthalate, tripropoxysilyl dioctyltin bis, dibutyltin bis-acetylacetone, dibutyltin stearate dioxide, carbomethoxyphenyl tin tris-uberate, isobutyltin triceroate, dimethyltin dibutyrate, dimethyltin dineodecanoate, triethyltin tartrate, dibutyltin dibenzoate, tin oleate , tin naphthenate, butyltin tri-2-ethylhexylhexoate, tin butyrate, diorganotin bis-diketonates, and the like. Useful titanium-containing catalysts include chelated titanium compounds, e.g., 1,3-propanedioxytitanium bis (ethylacetoacetate), di- bis (ethylacetoacetate). isopropoxy titanium and tetralakyl titanates, e.g., tetra-n-butyl titanate and tetra-isopropyl titanate. In yet another embodiment of the present invention, diorganotin bis-diketonates are used to facilitate entanglement in silicone seal composition. The inorganic-organic nanocomposites (d) of the present invention are comprised of at least one inorganic component which is a layered inorganic nanoparticle and at least one organic component which is a quaternary ammonium organopolysiloxane. When the invention is described, the following terms have the following meanings, unless otherwise indicated.

Definitions The term "exfoliation" as used herein, describes a process in which the nanoclay platelet bundles are separated from one another in a polymeric matrix. During the exfoliation, the platelets in the outermost region of each packet separation, exposing more platelets to the separation. The term "gallery" as used herein describes the separation between parallel layers of clay platelets. The separation of galleries changes depending on the nature of the molecule or polymer that occupies the space. An interspersed space between the individual nanoclay plates varies, depending again on the type of molecules that occupy the space. The term "intercalary" as used herein includes any inorganic or organic compound capable of entering the gallery of clays and bonding to its surface. The term "intercalary" as used in this, designates a clay-chemical complex where the separation of clay gallery has increased due to the process of surface modification. Under the appropriate conditions of temperature and shear, an interlayer is capable of exfoliating a resin matrix. As used herein, the term "interleaving" refers to a process to form an interleaving. The term "inorganic nanoparticle" as used herein describes a layered inorganic material, e.g., clay, with one or more dimensions, such as length, width, or thickness, on the nanoscale scale and which is able to undergo ion exchange. The expression "low gas permeability" as applied to the cured composition of this invention should be understood to mean an argon permeability coefficient not greater than about 9000"10 (STP) / cm sec (cmHg) measured according to the method of variable volume at constant pressure at a pressure of 7.03 kg / cm2 and temperature of 25 ° C. The term "modified clay" as used herein means a clay material, eg, nanoclay, which has been treated with any inorganic or organic compound that is capable of undergoing ion exchange reactions with the cations present from the inner layer surfaces of the clay The term "nanoclay" as used herein describes clay materials having a unique morphology With a nanometer scale dimension, nanoclays can form chemical complexes with an intercalant that bonds ionically to the surfaces between the layers that make up the particles. clay particles This association of intercalant and clay particles results in a material compatible with many different kinds of guest resins that allow the clay filter to disperse therein.

As used herein, the term "nanoparticles" refers to particle sizes, generally determined by diameter, less than about 1000 nm. As used herein, the term "platelets" refers to individual layers of the layered material. The inorganic nanoparticles of the present invention can be natural or synthetic such as smectite clay and should have certain ion exchange properties as in the smectite, rectorite, vermiculite, illite, micas and their synthetic analogues, including saponite, synthetic mica- monmorilonite and tetrasilicica mica. The nanoparticles can have a maximum average lateral dimension (width) in a first mode of between about 0.01 μm and about 10 μm, in a second mode between about 0.05 μm and about 2 μm, and in a third mode between about 0.1 μm and about 1 μm. The average maximum vertical (thickness) dimension of the nanoparticles can generally vary in a first mode between about 0.5 nm and about 10 nm and in a second mode between about 1 nm and about 5 nm. Useful inorganic nanoparticle materials of the invention include natural or synthetic phyllosilicates, particularly smectite clays such as montmorillonite, sodium montorilonite, calcium montmorillonite, magnesium montmorillonite, nontronite, beidelite, voldonscoite, saponite, hectorite, saponite, sauconite, magadite. , kenyaite, soboquita, svidordita, stevensite, talc, mica, kaolinite, vermiculite, halloisite, aluminate oxides, or hydrotalcites, micaceous minerals such as illite and illite / smectite minerals in mixed layers such as rectorite, tarosovite, lediquita and mixtures of illites with one or more of the clay minerals named above. Any material that can swell in layers that sufficiently absorbs organic molecules to increase the spacing of the interlayers between the phyllosilicate platelets adjacent to at least 5 angstroms, or at least about 10 angstroms, (when the phyllosilicate is dry) used to produce the inorganic-organic nanocomposite of the invention. The modified inorganic nanoparticles of the invention are obtained by contacting the quantities of inorganic particles in layers having interchangeable cations, e.g., Na +, Ca2 +, Al3 +, Fe2 +, Fe3 + and Mg2 +, with at least one organopolysiloxane containing ammonium. . The resulting modified particle is inorganic-organic nanocomposite (d) having intercalated organopolysiloxane ammonium ions.

The organopolysiloxane containing ammonium must contain at least one ammonium group and may contain two or more ammonium groups. The quaternary ammonium groups can be placed at the terminal ends of the organopolysiloxane and / or along the structure of the siloxane base. A class of organopolysiloxane containing ammonium has the general formula: MzDbD'c where "a" is 2, and "b" is equal to or greater than 1 and "c" is zero or positive; M is [R ^ NR ^ sx-yR ^ ySiOiz where "x" is 0, 1 or 2 and "y" is 0 or 1, subject to the limitation that x + y is less than or equal to 2, R1 and R2 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms; R3 is selected from the group consisting of the group consisting of H and a monovalent hydrocarbon group of up to 60 carbons; R4 is a monovalent hydrocarbon group of up to 60 carbons; D is R 5 R 6 SiO 2; wherein R5 and R6 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms; and D 'is R7R8Si02 2; wherein R7 and R8 each independently is a monovalent hydrocarbon group containing amine with the general formula: [R9'aNR10] wherein "a" is 2, R9 is selected from the group consisting of H and a monovalent hydrocarbon group up to 60 carbons, R10 is a monovalent hydrocarbon group of up to 60 carbons. In another embodiment of the present invention, the organopolysiloxane containing ammonium is R 11 R 12 R 13 N, wherein R 11, R 12 and R 13 are each independently an alkoxy silane or a monovalent hydrocarbon group of up to 60 carbons. The general formula for alkoxy silane is [R140] 3-xyR15? R16ySiR17 where "x" is 0, 1 or 2 and "y" is 0 or 1, subject to the limitation of x + y is less than or equal to 2; R14 is a monovalent hydrocarbon group of up to 30 carbons; R15 and R16 are monovalent hydrocarbon groups independently chosen from up to 60 carbons; R17 is a monovalent hydrocarbon group of up to 60 carbons. Additional compounds useful for modifying the inorganic component of the present invention are amine compounds or the corresponding ammonium ion with the structure R18R9R20N, wherein R18, R19 and R20 is each independently an alkyl or alkenyl group of up to 30 carbon atoms, and each independently is an alkyl or alkenyl group of up to 20 carbon atoms in another embodiment, which may be the same or different. In yet another embodiment, the organic molecule is a long chain tertiary amine wherein R18, R19 and R20 is each independently an alkyl or alkenyl of 14 carbons at 20 carbons. The layered inorganic nanoparticle compositions of the present invention do not need to be converted to a proton exchange form. Normally, the intercalation of an organopolysiloxane ammonium ion in the inorganic nanoparticle material in layers is achieved by cation exchange using solvent-free and solvent-based processes. In the solvent-based process, the organopolysiloxane ammonium component is placed in a solvent that is inert to the polymerization or coupling reaction. Particularly suitable solvents are water or water-ethanol, water-acetone and polar water-like co-solvent systems. By removing the solvent, the concentrates are obtained in intercalated particles. In the solvent-free process, a high shear mixer is usually required to carry out the intercalation reaction. The inorganic-organic nanocomposite can be in a suspension, gel, paste or solid form. A specific class of organopolysiloxanes containing ammonium are those described in the U.S. Patent. No. 5,130,396 all the content of which is incorporated by reference herein and may be prepared from known materials including those that are commercially available. The organosiloxanes containing ammonium of the U.S. Patent. No. 5,130,396 is represented by the general formula: wherein R1 and R2 are identical or different and represent a group of the formula: (ID wherein the nitrogen atoms in (I) are connected to the silicone atoms in (II) via the groups R5 and R5 represents an alkylene group with 1 to 10 carbon atoms, a cycloalkylene group with 5 to 8 atoms or a unit of the general formula: in which n is a number from 1 to 6 and indicates the number of methylene groups in the nitrogen position and m is a number from 0 to 6 and the free valences of the oxygen atoms attached to the silicon atom of other groups of the formula (II) and / or with the metal atoms of one or more of the interlacing binding bonds In which is a silicon, titanium or zirconium atom and R 'is a linear or branched alkyl group with 1 to 5 carbon atoms and the ratio of the silicon atoms of the groups of the formula (II) to the atoms of metals in the bonding bonds is 1: 0 a and in which R3 is equal to R1 or R2, or hydrogen, or a linear or branched alkyl group of 1 to 20 carbon atoms or is a cycloalkylene, benzyl, alkyl, propargyl group , chloroethylene, hydroxyethyl or chloropropyl consisting of 5 to 8 carbon atoms and X is an anion with the valence of x equal to 1 to 3 and selected from the halide group; hypochlorite, sulfate, hydrogen sulfate, nitrite, nitrate, phosphate, dihydrogen phosphate, carbonate, hydrogen carbonate, hydroxide, chlorate, perchlorate, chromate, dichromate, cyanide, cyanate, rhodanide, sulfur, hydrogen sulfide, selenide, telurate, borate, metaborate, azide, tetrafluroboborate, tetraphenylborate, hexafluorophosphate, formate, acetate, propionate, oxalate, trifluoroacetate, trichloroacetate or benzoate. The organopolysiloxane compounds containing ammonium described herein are microscopically spherical shaped particles with a diameter of 0.01 to 3.0 mm, a specific surface area of 0 to 1000 m2 / g, a specific pore volume of 0 to 5.0 ml / g, a volume density of 50 to 1000 g / l as well as a dry substance base in relation to the volume of 50 to 750 g / l. A method for preparing an organopolysiloxane containing ammonium involves reacting a primary, secondary or tertiary amylosiloxane having at least one hydrolysable alkoxy group, with water, optionally in the presence of an incatalyst to achieve hydrolysis and subsequent condensation of the silane and produce organopolysilane terminated at amine which is therefore quaternized with a suitable quaternizing reagent such as a mineral acid and / or alkyl halide to provide the organopolysiloxane containing ammonium. A method of this type is described in the U.S. Patent. No. 5,130,396 mentioned above. In this relation, the Patent of E.U.A. No. 6,730,766, all the contents of which are incorporated by reference herein, describe process for the manufacture of quaternized polysiloxane by the reaction of epoxy-functional polysiloxane. In a variation of this method, the primary, secondary or tertiary aminosilane having hydrolyzable alkoxy groups are quaternized prior to the hydrolysis condensation reactions giving the organopolsilyloxane. For example, N-trimethoxysilylpropyl-N, N, N-trimethylammonium chloride, N-trimethoxysilylpropyl-N, N, N-tri-n-butylammonium chloride and ocadecyldimethyl (3-trimethyloxysilylpropyl) ammonium chloride of trialkoxysilane containing ammonium commercially available (available from Gelest, Inc.) following its hydrolysis / condensation will provide organopolysiloxane containing ammonium for use herein. Another tertiary aminosilane suitable for preparing organopolysiloxane containing ammonium include tris (triethoxysilylpropyl) amine-tris (trimethoxysilylpropyl) amine, tris (diethoxymethylsilylpropyl) amine, tris (tripropoxysilylpropyl) amine, tris (ethoxydimethylsilylpropyl) amine, tris (triethoxyphenylsilylpropyl) amine; and similar. Yet another method for preparing the organopolysiloxane containing ammonium is to quaternize an organopolysiloxane containing primary, secondary or tertiary amine with quaternized reagent. Organopolysiloxanes containing amine include those of the general formula: wherein R1, R2, R6 and R7 each independently is H, hydrocarbyl of up to 30 carbon atoms, e.g., alkyl, cycloalkyl, aryl, alkaryl, aralkyl, etc., or R1 and R2 together or R6 and R7 together they form a divalent bridging group of up to 12 carbon atoms, R3 and R5 each independently is a divalent hydrocarbon linking group of up to 30 carbon atoms, optionally containing one or more oxygen and / or nitrogen atoms in the chain , e.g., straight or branched chain alkylene of 1 to 8 carbon atoms such as -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2C (CH3) -CH2-, -CH2CH2CH2CH2-, etc. each R4 independently is an alkyl group and n is from 1 to 20 and advantageously is from 6 to 12. These similar amine-containing organopolysiloxanes can be obtained by known and conventional methods, e.g., by reacting an olefinic amine such as allylamine with an polydiorganosiloxanes having Si-H bonds in the presence of a hydrosilation catalyst, such as platinum-containing hydrosilation catalyst as described in the US Patent No. 5,026,890, all the content of which is incorporated herein by reference. The specific amine-containing organopolysiloxanes which are useful for preparing the organopolysiloxanes containing ammonium include in this the commercial mixture of Optionally, the curable seal composition herein can contain at least one solid polymer (e) having a gas permeability that is less than the permeability of interlaced diorganopolysiloxane. Suitable polymers include polyethylenes such as low density polyethylene (LDPE), very low density polyethylene (VLDPE), low linear density polyethylene (LLDPE) and high density polyethylene (HDPE); polypropylene (PP), polyisobutylene (PIB), polyvinyl acetal (PVAc), polyvinyl alcohol (PVoH), polystyrene, polycarbonate, polyester, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), glycol modified polyethylene terephthalate (PETG); polyvinyl chloride (PVC), polyvinylidene chloride, polyvinylidene fluoride, thermoplastic polyurethane (TPU), styrene butadiene acrylonitrile (ABS) polymethyl methacrylate (PMMA), polyvinyl fluoride (PVF), polyamides (nylon), polymethylpentene, poly -imide (Pl), polyetherimide (PEI), polyether ether ketone (PEEK), polysulfone, polyether sulfonate, ethylene chlorotrifluoroethylene, polytetrafluoroethylene (PTFE), cellulose acetal, cellulose acetate butyrate, plasticized polyvinyl chloride, ionomer (Surtyn ), polyphenylene sulfide (PPS), styrene-maleic anhydride, modified polyphenylene oxide (PPO), and the like and mixtures thereof. The optional polymers may also be elastomeric in nature, examples include, but are not limited to, ethylene-propylene rubber (EPDM), polybutadiene, polychloroprene, polyisoprene, polyurethane (TPU), styrene-butadiene-styrene (SBS), styrene ethylene-butadiene-styrene (SEEBS), polymethylphenylsiloxane (PMPS), and the like. These optional polymers can be mixed alone or in combinations or in the form of copolymers, e.g., polycarbonate-ABS blends, polycarbonate polyester blends, grafted polymers such as silane grafted polyethylenes and silane grafted polyurethanes. In one embodiment of the present invention, the curable composition contains a polymer selected from the group consisting of low density polyethylene (LDPE), very low density polyethylene (VLDPE), low linear density polyethylene (LLDPE). , for its acronym in English), high density polyethylene (HDPE, for its acronym in English), and mixtures thereof. In another embodiment of the invention, the curable composition has a polymer selected from the group consisting of low density polyethylene (LDPE), very low density polyethylene (VLDPE), linear low density polyethylene (LLDPOE)., and mixtures thereof. In yet another embodiment of the present invention, the optional polymer is a linear low density polyethylene (LLDPE). The curable seal composition may contain one or more fillers in addition to the inorganic-organic nanocomposite component (d). Additional fillers suitable for use herein include precipitated and colloidal calcium carbonates which have been treated with compounds such as stearic acid or sterarate ester.; reinforcing silicas such as fumed silicas, precipitated silicas, silica gels and hydrophobic silicas and silica gels; crushed and milled quartz, alumina, aluminum hydroxide, titanium hydroxide, diatomaceous earth, iron oxide, carbon black, graphite, mica, talc and the like and mixtures thereof. The seal composition of the present invention may also include one or more alkoxysilanes as adhesion promoters. Useful adhesion promoters include N-2-aminoethyl-3-aminopropyltriethoxysilane, α-aminopropylethyl-methoxysilane, α-aminopropyltrimethoxysilane, aminopropyltrimethoxysilane, bis-β-trimethoxysilylpropyl) amine, N-phenyl-β-aminopropyltrimethoxysilane, triamino-functional tri-methoxysilane, α-aminopropylmethyldiethoxysilane ,? -aminopropilmetildietoxisilano, methacryloxypropyltrimethoxysilane, methylaminopropyltrimethoxysilane,? -glicidoxipropiletildimetoxisilano,? glycidoxypropyltrimethoxysilane,? -glicidoxietiltrimetoxisilano, ß- (3, 4-epoxycyclohexyl) propyltrimethoxysilane, ß- (3, 4-epoxycyclohexyl) etilmetildimetoxisilano, propyltriethoxysilane isocyanate isocianatopropilmetildimetoxisilano, ß- cyanoethyltrimethoxysilane,? -acyloxypropyltrimethoxysilane,? -methacryloxypropylmethyldimethoxysilane, 4-amino-3, 3-dimethylbutyltrimethoxysilane, and N-ethyl-3-trimethoxysilyl-2-methylpropanamine and the like. In one embodiment, the adhesion promoter may be a combination of n-2-aminoethyl-3-aminopropylmethoxysilane and 1,3,5-tris (trimethoxysilylpropyl) isocyanurate. The compositions of the present invention may also include one or more surfactants such as polyethylene glycol, polypropylene glycol, ethoxylated castor oil, oleic acid ethoxylate, alkylphenol ethoxylates, copolymers of ethylene oxide (EO) and propylene oxide (PO) and copolymers of silicones and polyethers (silicone-polyether copolymers), copolymers of silicones and copolymers of ethylene oxide and propylene oxide and mixtures thereof. The curable seal compositions of the present invention may still include other ingredients that are conventionally employed in compositions containing RTC silicone such as colorants, pigments, plasticizers, antioxidants; UV stabilizers, biocides, etc., in known and conventional amounts as long as they do not interfere with the properties desired for the cured compositions. The amounts of silanol-terminated diorganopolysiloxanes, interlacing, entanglement catalysts, inorganic-organic nanocomposites, optional solid polymers of lower gas permeability than interlaced diorganopolysiloxanes, optional fillers other than inorganic-organic nanocomposites, optional adhesion promoters and ionic surfactants optionals can vary widely and, advantageously, can be selected from among the scales indicated in the following table. The curable compositions herein contain inorganic-organic nanocomposites in an amount, of course, that enhances their gas barrier properties.

Table 1: Quantity Scales (percent by weight) of Components of the Curable Composition of the Invention Components of the. scale 2a. scale 3a. scale Composition Curable Diorganopolysiloxane 50-99 70-99 80-85 finished in silanol Interleavers 01-10 0.3-5 0.5-1.5 Catalysts 0.001-1 0.003-0.5 0.005-0.2 Interlacing Nanocomposites 0.1-5 10-30 15-20 inorganic-organic Solid polymers 0-50 5-40 10-35 Gas permeability lower than interlaced diorganopolysiloxane Different fillings 0-90 5 -60 10-40 to inorganic-organic nanocomposites Promoters of 0-20 0.1-10 0.5-2 silane adhesion Agents 0-10 0.1-5 0.5-0.75 ionic surfactants Curable sealant compositions can be obtained herein by methods that are well known in the art, e.g., melt mix, extrusion blends, solution mix, dry mix, mix in a Banbury mixer, etc., in presence of moisture to give a substantially homogeneous mixture. Preferably, the methods for mixing the diorganopolysiloxane polymers with polymers can be achieved by contacting the components in a stirrer or other physical mixing means, followed by melt blending in an extruder. Alternatively, the components can be melt-blended directly in an extruder, Brabender or any other means of melt mixing. The cured seal composition 7 is obtained by curing the curable composition obtained by mixing (a) at least one diorganopolysiloxane, (b) at least one interleaver for the diorganopolysiloxane, (c) at least one catalyst for the interlacing reaction, (c) d) at least one inorganic-organic nanocomposite and, optionally, (e) at least one solid polymer having a gas permeability that is less than the permeability of the interlaced diorganosiloxanes, the composition after curing exhibiting low permeability to gases The invention is illustrated by the non-limiting examples.

COMPARATIVE EXAMPLE 1 AND EXAMPLES 1-2 The inorganic-organic nanocomposite was prepared by first placing 10 g of finished aminopropyl siloxane ("GAP 10", Siloxane length of 10, GE Silicones, Waterford, USA) in a single neck round bottom flask and adding 4 ml of methanol available from Merck. 2.2 ml of concentrated HCl was added very slowly with stirring. Stirring continued for 10 minutes. 900 ml of water were added to a 2000 ml three-necked round bottom flask fitted with condenser and top mechanical stirrer. 10 g of Na + Cloisite clay (natural montmorillonite available from Southern Clay Products) is added to the water very slowly with stirring (agitation rate of about 250 rpm). The ammonium chloride solution (prepared above) was then added very slowly to the clay-water mixture. The mixture was stirred for 1 hour and allowed to stand overnight. The mixture was filtered through a Buckner funnel and the solid obtained was covered with 800 ml of methanol, stirred for 20 minutes and then the mixture was filtered. The solid was dried in an oven at 80 ° C for about 50 hours. To give a nanocomposite of 2.5 weight percent, 224.25 g of OMCTS (octamethylcyclotetrasiloxane) and 5.75 g of modified clay of GAP 10 (inorganic-organic nanocomposite prepared before 9) was introduced into a three neck round bottom flask adapted with stirrer The mixture was stirred at 250 rpm for 6 hours at room temperature, the temperature was increased to 175 ° C while stirring continued, 0.3 g of CsOH in 1 ml of water was added to the reaction vessel through the septum. After 15 minutes, polymerization of OMCTS started and 0.5 ml of water was added with an additional 0.5 ml of added water after 5 minutes.The heating and stirring continued for 1 hour after which it was added to phosphoric acid for neutralization. The pH of the reaction mixture was determined after 30 minutes. Stirring and heating were continued for another 30 minutes and the pH of the reaction mixture again determined to ensure complete neutralization. The cyclic distillation was carried out at 175 ° C and the mixture was then cooled to room temperature. The same procedure was followed with 5 weight percent modified GAP 10 clay. Polymerization procedures in situ with 2.5 wt% and 5 wt% (see Table 1) of GAP 10 modified clays (prepared above) were followed. . Polymers in situ with different amounts of clay were then used to form cured sheets in the following manner: polydimethylsiloxanes terminated in silanol in situ (PDMS), (Silanol 5000, a silanol-terminated polydimethylsiloxane of nominal 5000 cs and Silanol 50,000, a silanol-terminated polydimethylsiloxane of nominal 50,000 cs, both available from Gelest, Inc.), the modified clay formulations of GAP 10 were mixed with NPS interleaver (n-propyl silicate, available from Gelest, Inc.) solubilized DBTO catalyst (solubilized dibutyl tin oxide, available from GE silicones, Waterford USA) using a hand mixer for 5-7 minutes the air bubbles being removed to empty. The mixture was then poured into a Teflon sheet forming mold and maintained for 24 hrs under ambient conditions (25 ° C and 50% humidity). The cured sheets were partially removed from the mold after 24 hours and kept at room temperature for seven days for complete cure.

Table 1 grams% p% p NPS DBTO Comparative example 1: 50 2 1.2 Silanol Example 1: silanol with 2.5% weight of 50 2 1.2 modified clay Example 2: Silanol with 5% by weight of 50 2 1.2 s rr i l ls mnH i i rsrls The permeability of Argon was measured using an established gas permeability. The permeability of argon was measured using gas permeability established as in the previous examples. Previous measurements were based on a variable volume method at a pressure of 7.03 kg / cm2 and at a pressure of 25 ° C. Measurements were repeated under identical conditions 2-3 times in order to ensure reproduction. The permeability data for Comparative Example 1 and Examples 1 and 2 are presented grcally in Figure 2.

COMPARATIVE EXAMPLE 2 AND EXAMPLE 3 Example 3 (see Table 2) was prepared by mixing 45 grams of PDMS and 5 grams of GAP 10 modified clay (prepared above) and similar in situ polymerization procedures were followed by mixing with 2% NPS weight, and 1.2% weight of DBTO, using a manual mixer for 5-7 minutes, air bubbles being removed by vacuum. Each mixture was poured into a sheet forming mold and held for 24 hours under ambient conditions (25 ° C and 50% humidity) to partially cure the PDMS components. The partially urinated leaves were removed from the mold after 24 hours and kept at room temperature for seven days for complete cure.

Table 2 grams% p% p NPS DBTO Comparative Example 1: mixture of 50 1.2 silanol Example 3: silanol with 5% weight of 50 1.2 modified clay The permeability of argon was measured using a gas permeability established as in the previous examples. The measurements were based on the variable volume method at a pressure of 7.03 kg / cm2 and at a temperature of 25 ° C. The measurements were repeated under identical conditions 2-3 times in order to ensure their reproduction. The permeability data for Comparative Example 2 and Example 3 are presented grcally in Figure 3.

COMPARATIVE EXAMPLE 3 AND EXAMPLES 4 AND 5 The inorganic-organic nanocomposite of Examples 4 and 5 were prepared by introducing 15 grams of octadecyldimethyl (3-trimethoxysilylpropyl) ammonium chloride (available from Gelest, Inc.) in a 100 ml agitator and slowly adding 50 ml of methanol (available from Merck). grams of Cloisite 15A clay ("C-15A", a modified montmorillonite clay with 125 milliequivalents of dimethyl dehydrogenated tallow ammonium chloride per 100 g of clay available from Southern Clay Products) was added very slowly to a 5-well stirrer. liters containing a water: methanol solution (ratio of 1: 3, 3.5 1) and equipped with an overhead mechanical stirrer that agitated the mixture at a rate of approximately 400 rpm. Stirring continued for 12 hours. The octadecyldimethyl (3-trimethoxysilyl propyl)) chloride (prepared above) was then slowly added. The mixture was stirred for 3 hours. The mixture was then filtered through a Buckner funnel and the solid obtained was washed with a solution of water: methanol (1: 3) several times before being filtered again. The solid was dried in an oven at 80 ° C for about 50 hours. The mixtures indicated above were then used to form cured sheets in the following manner: PDMS-silylpropyl-modified clay formulations were mixed with NPS and DBTO, as listed in Table 3, using a manual mixer for 5-7 minutes being The air bubbles are removed by vacuum. Each mixture was poured into a Teflon sheet forming mold and kept for 24 hours under ambient conditions (25 ° C and 50% humidity) to partially cure the PDMS components. The cured sheets were partially removed from the mold after 24 hours and kept at room temperature for seven days for complete cure.

Table 3 grams% p% p NPS DBTO Comparative Example 3: Mixture of silanol 50 2 1. 2 Example 4: silanol with 5 phr of clay 50 2 1. 2 modified with silylpropyl Example 5: Silanol mixture with 10 phr 50 2 1.2 clay modified with silylpropyl The permeability of Argon was measured using gas permeability established as in the previous examples. The measurements were based on the variable volume method at a pressure of 7.03 kg / cm2 and at a temperature of 25 ° C. The measurements were repeated under identical conditions 2-3 times in order to ensure their reproduction. The permeability data for Comparative Example 3 and Examples 4 and 5 are presented graphically in the Figure. The permeability data are presented graphically in Figures 2, 3 and 4. As shown in the data, the permeability of argon in the chaos of cured seal compositions of the invention (Examples 1 and 2 of Figure 2, Example 3 of Figure 3 and Examples 4 and 5 of Figure 4) was significantly less than that of cured seal compositions outside the scope of the invention (Comparative Examples 1-3 of Figures 2-4, respectively). In all, the argon permeability coefficients of the seal compositions of Comparative Examples 1, 2 and 3 exceeded 950 barriers, those of Examples 1-5 illustrating the seal compositions of this invention do not exceed 875 barriers and in some cases, they are below this level of argon permeability coefficient (see, in particular, examples 2, 4 and 5). While the preferred embodiment of the present invention has been illustrated and described in detail, various modifications of, for example, components, materials and parameters, will be apparent to those skilled in the art, and are intended to cover the appended claims, all the Modifications and changes will be within the scope of this invention.

Claims (22)

1. - An insulated glass unit comprises at least two separate glass sheets in spaced relation each, a low thermal conductivity insulation gas or a mixture of the gases that are between them and a gas seal element that includes a composition Cured seal resulting from curing of the curable seal composition comprises: a) at least one diorganopolysiloxane terminated in silanol; b) at least one interlayer for the diorganopolysiloxane terminated in silanol; c) at least one catalyst for the crosslinking reaction; d) a gas barrier that increases the amount of at least one inorganic-organic nanocomposite, and optionally, e) at least one solid polymer having gas permeability that is less than the permeability of the interlaced diorganopolysiloxane. 2. The isolated glass unit of claim 1, wherein the diorganopolysiloxane terminated in silanol (a) has the general formula:

MzDbD'c where "a" is 2, and "b" is equal to or greater than 1 and "c" is zero or positive; M is (HO -x-yR'xR'ySiOl / Z where "x" is 0, 1 or 2 and "y" is 0 or 1, subject to the limitation that x + y is less than or equal to 2 , R1 and R2 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms, D is R3R4Si01 2, wherein R3 and R4 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms, and D1 is R5R6Si02 2; wherein R5 and R6 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms

3. The isolated glass unit of claim 1, wherein the interlayer (b) is an alkyl silicate having the formula: : (R140) (R150) (R170) If where R14, R15, R16 and R17 are each independently a monovalent hydrocarbon group of up to 60 carbon atoms

4. The isolated glass unit of claim 1, wherein the catalyst (c) is a tin catalyst.

5. -The isolated glass unit of the claim 4, wherein the tin catalyst is selected from a group consisting of dibutyltin dilaurate, dibultiltin diacetate, dibutyltin dimethoxide, tin octoate, isobutyltin triceroate, dibutyltin oxide, soluble dibutyltin oxide, bis-di-isooctylphthalate of dibutyltin, tripropoxysilyl dioctyltin bis, dibutyltin bis-acetylacetone, dibutyltin stearate dioxide, carbomethoxyphenyl tin tris-uberate, isobutyltin triceroate, dimethyltin dibutyrate, dimethyltin dineodecanoate, triethyltin tartrate, dibutyltin dibenzoate, tin oleate, naphthenate of tin, butyltin tri-2-ethylhexylhexoate, tin butyrate, diorganotin bis-diketonates and mixtures thereof.

6. The isolated glass unit of claim 1, wherein the inorganic or organic nanocomposite comprises at least one organic component which is an inorganic layered nanoparticle and at least one organic component which is a layered inorganic nanoparticle and at least one organic component which is a quaternary ammonium organopolysiloxane.

7. - The inorganic or organic nanocomposite of claim 6, wherein the layered inorganic nanoparticle has an exchangeable cation which is at least one member selected from a group of Na +, Ca 2+, Al 3+, Fe 2+, Fe3 +, Mg2 + and mixtures thereof.

8. The isolated glass unit of claim 6, wherein the layered nanoparticle is at least one member selected from a group consisting of montmorillonite, sodium montorilonite, calcium montmorillonite, magnesium montmorillonite, nontronite, beidelite, voldonscoite, saponite, hectorite, saponite, sauconite, magadite, kenyaite, soboquita, svidordite, stevensite, talc, mica, kaolinite, vermiculite, halloisite, aluminate oxides, or hydrotalcites, illite, rectorite, tarosovite, lediquita and mixtures thereof.

9. The isolated glass unit of claim 6, wherein the quaternary ammonium organopolysiloxane is at least one ammonium-containing diorganopolysiloxane having the formula of: MzDbD'c where "a" is 2, and "b" is equal to or greater than 1 and "c" is zero or positive; M is [R32NR4] 3.x_yR1xR2ySi01 / 2 where "x" is 0, 1 or 2 and "y" is 0 or 1, subject to the limitation that x + y is less than or equal to 2, R1 and R2 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms; R3 is selected from the group consisting of the group consisting of H and a monovalent hydrocarbon group of up to 60 carbons; R4 is a monovalent hydrocarbon group of up to 60 carbons; D is R 5 R 6 SiO 2; wherein R5 and R6 each independently is a monovalent hydrocarbon group of up to 60 carbon atoms; and D1 is R7R8Si02 2; wherein R7 and R8 each independently is a monovalent hydrocarbon group containing amine with the general formula: [R9'aNR10] wherein "a" is 2, R9 is selected from the group consisting of H and a monovalent hydrocarbon group up to 60 carbons, R10 is a monovalent hydrocarbon group of up to 60 carbons.

10. The inorganic or organic nanocomposite of claim 9, wherein the quaternary ammonium group is represented by the formula R6R7R8N + X ", wherein at least one R6 'R7 and R8 is alkoxyl silane of 60 carbon atoms and the remainder is of an alkyl or alkenyl group of 60 carbon atoms and X is an anion

11. The isolated glass unit of claim 1, wherein the solid polymer (e) is selected from a group consisting of low density polyethylene, very low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, polyisobutylene, polyvinyl acetate, polyvinyl alcohol, polystyrene, polycarbonate, polyester, such as polyethylene terephthalate, polybutylene terephthalate , polyethylene naphthalate, modified glycol polyethylene terephthalate, polyvinylchloride, polyvinylidene chloride, fluorinated polyvinyldene, thermoplastic polyurethane, acrylonitrile butadiene styrene, poly ethyl methacrylate, polyvinyl fluoride, polyamides, polymethylpentene, polyamide, polyetherimide, polyether ether ketone, polysulfone, polyether sulfonate, ethylene chlorotrifluoroethylene, polytetrafluoroethylene, cellulose acetate, cellulose acetate butyrate, plasticized polyvinylchloride, ionomers, sulfite of polyphenylene, styrene maleic anhydride, modified polyphenylene oxide, ethylene propylene rubber, polybutadiene, polychloroprene, polyisoprene, polyurethane, styrene-butadiene-styrene, styrene-ethylene-butadiene-styrene, polymethylphenyl siloxane and mixtures thereof.

12. The isolated glass unit of claim 1, wherein it further comprises at least one optional component selected from a group consisting of an adhesion promoter, surfactant, dye, pigment, plasticizer, a filler other than the inorganic nanocomposite or organic, antioxidant, UV stabilizer and biocide.

13. The isolated glass unit of claim 12, wherein the adhesion promoter is selected from a group consisting of n-2-aminoethyl-3-aminopropyltrimethoxysilane, 1,3,5-tris (trimethoxysilylpropyl) isocinaurate,? -aminoprpiltrietoxisilano, aminopropyltrimethoxysilane, aminopropyltrimethoxysilane, bis -trimetoxisilipropil) amine, N-phenyl aminopropyltrimethoxysilane, functional triaminotrimetoxisilano, -aminopropilmetildietoxisilano, -aminopropilmetildietoxisilano, metacriloxipropiltrimetildietoxisilano, methylaminopropyltrimethoxysilane, -glicidoxipropiletildimetoxisilano, glycidoxypropyltrimethoxysilane,???????? - glycidoxyethyltrimethoxysilane, ß- (3, 4-epoxycyclohexyl) propyltrimethoxysilane, ß- (3 -epoxiciclohexil) etilmetildimetoxisilano, isocyanatopropyltriethoxysilane, ß- (3, 4-epoxycyclohexyl) etilmetildimetoxisilano, isocyanatopropyltriethoxysilane, isocianatopropilmetildimetoxilsilano, beta-cyanoethyltrimethoxysilane, -acriloxipropiltrimetoxisilano,? - metacriloxipro pilmetyldimethoxysilane, 4-amino-3, 3, -dimethylbutyltrimethoxysilane, n-ethyl-3-trimethoxysilyl-2-methylpropanoamine and mixtures thereof.

14. The insulated glass unit of claim 12, wherein the surfactant is a nonionic surfactant selected from a group consisting of polyethylene glycol, polypropylene glycol, ethoxylated castor oil, oleic acid ethoxylate, ethoxylates. of alkylphenol, copolymers of ethylene oxide and propylene oxides and copolymers of silicones and polyethers, copolymers of silicones and copolymers of ethylene oxide and propylene oxide and mixtures thereof.

15. The isolated glass unit of claim 14, wherein the nonionic surfactant is selected from a group consisting of copolymers of ethylene oxide and propylene oxide, copolymers of silicones and polyethers, copolymers of silicones and copolymers of ethylene oxide and propylene oxide and mixtures thereof.

16. The isolated glass unit of claim 12, wherein the filler is other than the inorganic or organic nanocomposite that is selected from a group consisting of calcium carbonate, precipitated calcium carbonate, colloidal calcium carbonate, carbonate Calcium treated with stearate or stearic acid compounds, fumed silica, precipitated silica, silica gel, hydrophobic silicas, silica gel hydrophilites, crushed quartz, granulated quartz, alumina, aluminum hydroxide, titanium hydroxide, clay, kaolin, montmorilinonite bentonite, diatomaceous earth, iron oxide, black carbon and graphite, mica, talc and mixtures thereof.

17. The isolated glass unit of claim 1, wherein MaDbD'c where "a" is 2 and "b" is equal to or better than 1 and "c" is zero or positive; M is (HO -x-yR'xR'ySÍOiz where "x" is 0, 1 or 2 and "y" is either 0 or 1, subject to the limitation that x + y is less than or equal to 2, R1 and R2 each independently is a monovalent hydrocarbon group of 60 carbon atoms, D is R3R4SiO ?2, wherein R3 and R4 each independently is a monovalent hydrocarbon group of 60 carbon atoms, and D is R5R6Si022 wherein R5 and R6 each independently is a monovalent hydrocarbon group of 60 carbon atoms, the interlayer (b) is an alkylsilicate has the formula: (R140) R150) (R160) (R170) Where R? , R15, Ri6 and R? they are chosen independently of monovalent hydrocarbon radicals the catalyst (c) is a tin catalyst; and the inorganic nanoparticle portion is an inorganic or organic nanocomposite (d) which is selected from a group consisting of montmorillonite, sodium montmorillonite, calcium montmorillonite, magnesium montmorillonite, nontronite, beidelite, volkonskoite, saponite, hectorite, saponite, sauconite, magadite, kenyaite, soboquita, svindordite, stevensite, vermiculite, halosite, aluminate oxides, hydrotalcite, illite, rectorite, tarosovite, ledikitekaolinita and mixtures thereof, the organic portion of the inorganic or organic nanocomposite (d) has been so minus one quaternary ammonium compound R6R7R8N + X ", wherein at least one R6 'R7 and R8 is alkoxyl silane of 60 carbon atoms and the remainder is of an alkyl or alkenyl group of 60 carbon atoms and X is a anion

18. The insulated glass unit of claim 1, wherein the isolating gas is selected from a group consisting of air, carbon dioxide, sulfur hexafluoride, nitrogen, argon, krypton, xenon and mixtures thereof.

19. The insulated glass unit of claim 1, wherein the cured sealing composition upon curing exhibits an argon permeability coefficient not greater than 900 barriers.

20. The insulated glass unit of claim 11, wherein the cured sealing composition upon curing exhibits an argon permeability coefficient not greater than 900 barriers.

21. The insulated glass unit of claim 12, wherein the cured sealing composition upon curing exhibits an argon permeability coefficient not greater than 900 barriers.

22. The isolated glass unit of claim 17, wherein the cured sealing composition upon curing exhibits an argon permeability coefficient not greater than 900 barriers.