WO2007029942A1

WO2007029942A1 - System and method for closing tank opening

Info

Publication number: WO2007029942A1
Application number: PCT/KR2006/003487
Authority: WO
Inventors: Myung-Ho Kim; Minki Kim; Sehyun Kim; Youngtock Oh; Jaeyong Shin; Youngchul Yang
Original assignee: Lg Chem, Ltd.
Priority date: 2005-09-07
Filing date: 2006-09-04
Publication date: 2007-03-15
Also published as: TWI333464B; KR20070028173A; TW200720411A

Abstract

Disclosed herein is a system for sealing an opening of a tank. The system comprises a plate which includes a layer formed of a nanocomposite composition having barrier properties, which is prepared by dry-blending a polyolefin resin, a nanocomposite having barrier properties and a compatibilizer. The system shows superior gas- and liquid-barrier properties. Further disclosed is a method for sealing an opening of a tank.

Description

SYSTEM AND METHOD FOR CLOSING TANK OPENING

Technical Field

[1] The present invention relates to a system with superior barrier properties for sealing an opening of a tank and a method for sealing an opening of a tank. Background Art

[2] General-purpose resins, such as polyethylene and polypropylene, are currently used in various applications for their good moldability, excellent mechanical properties and superior moisture-barrier properties. However, these resins have limited applicability to liquid and gas tanks that require hydrocarbon-barrier properties. For this limitation, multilayer structures formed by co-extrusion, lamination or coating of general-purpose resins and other resins have been used instead. At present, ethylene- vinyl alcohol copolymers and polyamide resins are used to manufacture multilayer molded plastic articles requiring barrier properties due to their superior gas-barrier properties. However, ethylene- vinyl alcohol copolymers and polyamide resins are more expensive than general-purpose resins. There is thus a continued need for a resin composition that has superior barrier properties despite the use of a reduced amount of an ethylene- vinyl alcohol copolymer or a polyamide resin.

[3] On the other hand, liquid or gas tanks used in on board vehicles of various types must generally meet standards for tightness and permeability related to the type of use for which they are designed and the environmental requirements with which they must comply. At the present time, both in Europe and in the world, the requirements regarding the limitation of emissions of pollutants into the atmosphere and into the environment in general are being considerably tightened. The design of liquid and gas tanks is consequently undergoing rapid development towards using techniques capable of better guaranteeing sealing and safety under a variety of operating conditions. Moreover, it is also endeavored to reduce as far as possible any losses arising from the various accessories and pipes associated with the tanks. One means sometimes used has been to incorporate certain accessories and pipes within the tanks, thus eliminating their interfaces with the external atmosphere.

[4] It is known, from Patent Application WO 01/21428 by SOLVAY, to close off an opening in a multilayer tank by means of a multilayer plastic plate welded to the wall of the tank so as to cover the opening, the layer of plastic of the plate welded to the tank having a composition compatible with the surface layer of the tank.

[5] In the tank described in that patent application, there remains, however, a fuel permeation pipe located between the barrier layer, with which the inside of the multilayer structure of the closure plates is generally provided, and the wall of the tank, the pipe being made of a plastic, such as HDPE, the impermeability to fuel of which is not optimal.

[6] According to the prior art, since the layer of plastic of the plate must be compatible with the surface layer of the tank, it is essential to form a multilayer structure consisting of the barrier layer and the surface layer. Further, there is a problem in that the plastic material for the layer of the plate is limited to that constituting the tank. For example, in the case where the surface layer of the tank is formed of HDPE, the layer of the plate is formed of HDPE having poor barrier properties, causing a danger of fuel leakage through the welded face between the surface layer of the tank and the layer of the plate.

Disclosure of Invention Technical Problem

[7] Therefore, it is one object of the present invention to provide a system and a method for sealing an opening of a fuel tank that use a plate made of a nanocomposite blend having superior gas- and liquid-barrier properties even in a monolayer structure and compatible with an external layer of a wall of a fuel tank, thereby inhibiting fuel leakage through the welded face between the plate and the wall of the fuel tank. Technical Solution

[8] In accordance with one aspect of the present invention for achieving the above object, there is provided a system for sealing an opening of a tank, the system comprising a plate welded to a wall of a tank at the location of the periphery of an opening of the tank wherein the plate includes a layer formed of a nanocomposite composition having barrier properties, the nanocomposite composition being prepared by dry-blending (a) 100 parts by weight of a polyolefin resin, (b) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene-vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcohol,and (c) 1 to 30 parts by weight of a compatibilizer.

[9] In one embodiment of the present invention, the polyolefin resin may be selected from the group consisting of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, an ethylene-propylene copolymer, metallocene polyethylene, polypropylene, and mixtures thereof. The polypropylene may be selected from the group consisting of a homopolymer and a copolymer of propylene, metallocene polypropylene, and a composite resin, which is prepared by adding at least one additive selected from talc, flame retardants and the like to a homopolymer or copolymer of propylene to reinforce the physical properties of the polypropylene ho- mopolymer or copolymer.

[10] In a further embodiment of the present invention, the layered clay may be selected from the group consisting of montmorillonite, bentonite, kaolinite, mica, hectorite, flu- orohectorite, saponite, beidellite, nontronite, stevensite, vermiculite, hallosite, volkonskoite, suconite, magadite, kenyalite, and mixtures thereof.

[11] In a further embodiment of the present invention, the polyamide may be selected from 1) nylon 46, 2) nylon 6, 3) nylon 66, 4) nylon 610, 5) nylon 7, 6) nylon 8, 7) nylon 9, 8) nylon 11, 9) nylon 12, 10) nylon 46, 11) MXD6, 12) amorphous polyamide, 13) a polyamide copolymer containing two or more polyamides of the polyamides 1) to 12), and 14) mixtures of two or more polyamides of the polyamides 1) to 12).

[12] In another embodiment of the present invention, the ionomer may have a melt index ranging from 0.1 to 10 g/10 min (190°C, 2,16Og).

[13] In another embodiment of the present invention, the compatibilizer may be at least one copolymer selected from the group consisting of an ethylene-ethylene anhydride- acrylic acid copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-alkyl acrylate-acrylic acid copolymer, maleic anhydride modified (graft) high-density polyethylene, maleic anhydride modified (graft) linear low-density polyethylene, an ethylene-alkyl methacrylate-methacrylic acid copolymer, an ethylene-butyl acrylate copolymer, an ethylene- vinyl acetate copolymer, and a maleic anhydride modified (graft) ethylene- vinyl acetate copolymer.

[14] In another embodiment of the present invention, the plate may be provided with at least one pipe penetrating the plate.

[15] In another embodiment of the present invention, the plate may be attached to at least one accessory positioned inside the tank.

[16] In yet another embodiment of the present invention, the plate may have a multilayer structure.

[17] In accordance with another aspect of the present invention, there is provided a method for sealing an opening of a tank, the method comprising the steps of: (a) dry- blending (i) 100 parts by weight of a polyolefin resin, (ii) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcoholand (iii) 1 to 30 parts by weight of a compatibilizer to prepare a nanocomposite composition having barrier properties; (b) producing a plate, which includes a layer formed of the nanocomposite composition, by molding; and (c) welding the plate to periphery of an opening of a tank to seal the opening.

[18] In one embodiment of the present invention, the plate may be welded to the opening of the tank by hot-plate welding, vibration welding, or laser welding.

[19] In a further embodiment of the present invention, at least one accessory may be welded to the plate before the plate provided with at least one accessory is welded to the periphery of the opening.

[20] In another embodiment of the present invention, at least one accessory may be attached to the internal wall of the tank adjacent to the opening before the tank is sealed by simultaneously welding the plate to the accessory and the periphery of the opening.

[21] In another embodiment of the present invention, the tank may be a fuel tank for a motor vehicle. Brief Description of the Drawings

[22] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

[23] FlG. 1 is a cross-sectional view schematically showing a system for sealing an opening of a tank according to the present invention. Mode for the Invention

[24] The present invention will now be described in more detail.

[25] The term "tank" is understood to mean a closed chamber, of various shapes, generally sealed with respect to the outside, which may be equipped with various accessories positioned inside the chamber or passing through its wall. The tank may be a gas tank, a liquid tank or a tank designed to contain both a gas and a liquid. Preferably, the tank may be a liquid tank or a liquid tank containing also a gaseous phase.

[26] Certain tanks have one or more openings, that is to say, cut-outs of circular or other shape, made through the wall of the tank for various purposes, for example so as to be able to introduce at least one accessory into the tank that cannot be incorporated therein during its manufacture.

[27] In order to be able to use the tank for its normal usage of storing and containing liquid and gas, it is necessary to design and adapt a sealing system capable of sealing the tank as hermetically as possible after the insertion of the accessory.

[28] The present invention provides a system for sealing an opening of a tank, the system comprising a plate wherein the plate includes a layer formed of a composition, the composition being prepared by dry-blending (a) 100 parts by weight of a poly olefin resin, (b) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcohol,and (c) 1 to 30 parts by weight of a compatibilizer. [29] The sealing system of the present invention is designed for a plastic tank with a monolayer or multilayer structure. The term "plastic" is understood to include synthetic polymers, thermoplastic and thermosetting materials that are in the solid state under the ambient conditions, and to include mixtures of at least two of these materials. The polymers include homopolymers and copolymers. The tank is preferably made of a resin having barrier properties. In the case where the tank has a multilayer structure, at least one internal layer is preferably a barrier layer. Non-limiting examples of such barrier compositions are polyamide and copolyamide resins, copolymers of statistic ethylene and vinyl alcohol, and thermotropic liquid crystal polymers, such as copolyesters of p-hydroxybenzoic acid and either 6-hydroxy-2-naphthoic acid or terephthalic acid and 4,4'-biphenol.

[30] More preferably, the plastic tank has the same composition as the plate of the sealing system according to the present invention. That is, the tank may have a monolayer or multilayer structure that includes a layer formed of a composition, the composition being prepared by dry-blending (a) 100 parts by weight of a poly olefin resin, (b) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcohol,and (c) 1 to 30 parts by weight of a compatibilizer.

[31] The term "plate" indicates any solid member of small thickness relative to its surface area and whose rigidity is similar to that of the walls of the tank. The plate can have various shapes; most often, the shape of the plate depends on the various types of tanks and on the location of the opening to be sealed on the surface of these tanks. The plate often has a surface that is flat or curved slightly inward, particularly in the case of an opening with small dimensions such as, for example, circular openings whose diameter does not exceed 80 mm.

[32] In the sealing system of the present invention, as the polyolefin resin, there can be used a resin selected from the group consisting of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), an ethylene-propylene copolymer, metallocene polyethylene, polypropylene, and mixtures thereof. The polypropylene may be selected from the group consisting of a ho- mopolymer and a copolymer of propylene, metallocene polypropylene, and a composite resin, which is prepared by adding at least one additive selected from talc, flame retardants and the like to a homopolymer or copolymer of propylene to reinforce the physical properties of the polypropylene homopolymer or copolymer.

[33] In the sealing system of the present invention, the nanocomposite having barrier properties is prepared by mixing a layered clay with at least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol (EVOH) copolymer, polyamide, an ionomer and polyvinyl alcohol (PVA). The nanocomposite having barrier properties thus prepared possesses a morphology selected from fully exfoliated, partially exfoliated, intercalated, and partially intercalated forms. The most important thing is to maintain the morphology of the nanocomposite having barrier properties even after completion of molding. Preferably, a fully exfoliated form is advantageous in improving the barrier properties of the nanocomposite.

[34] The weight ratio of the resin having barrier properties to the layered clay in the nanocomposite having barrier properties is in the range of 58.0: 42.0 to 99.9: 0.1 and preferably 85.0: 15.0 to 99.0: 1.0. When the resin having barrier properties is present in an amount of less than 58.0% by weight, the layered clay aggregates and is thus not suitably dispersed in the nanocomposite having barrier properties. Meanwhile, when the resin having barrier properties is present in an amount exceeding 99.9% by weight, an improvement in barrier properties is undesirably negligible.

[35] The layered clay is preferably organically modified by intercalating an organic modifier between layers of the layered clay. The content of the organic modifier in the layered clay is preferably in the range of 1 to 45% by weight. The use of the organic modifier in an amount of less than 1% by weight causes poor compatibility between the layered clay and the resin having barrier properties. Meanwhile, the use of the organic modifier in an amount exceeding 45% by weight makes it difficult to intercalate chains of the resin having barrier properties between layers of the layered clay.

[36] The layered clay is preferably selected from the group consisting of montmo- rillonite, bentonite, kaolinite, mica, hectorite, fluorohectorite, saponite, beidellite, nontronite, stevensite, vermiculite, hallosite, volkonskoite, suconite, magadite, kenyalite, and mixtures thereof. The organic modifier is preferably an organic material having a functional group selected from the group consisting of primary ammonium, secondary ammonium, tertiary ammonium, quaternary ammonium, phosphonium, maleate, succinate, acrylate, benzylic hydrogen, oxazoline, and distearyldimethy- lammonium groups.

[37] The content of ethylene in the ethylene-vinyl alcohol copolymer used in the present invention is preferably from 10 to 50 mol%. When the ethylene content is lower than 10 mol%, melt-molding of the final composition becomes difficult due to poor pro- cessability. Meanwhile, when the ethylene content is higher than 50 mol%, sufficient oxygen- and liquid-barrier properties are not achieved.

[38] The polyamide may be selected from 1) nylon 46, 2) nylon 6, 3) nylon 66, 4) nylon

610, 5) nylon 7, 6) nylon 8, 7) nylon 9, 8) nylon 11, 9) nylon 12, 10) nylon 46, 11) MXD6, 12) amorphous polyamide, 13) a polyamide copolymer containing two or more polyamides of the polyamides 1) to 12), and 14) mixtures of two or more polyamides of the polyamides 1) to 12).

[39] The term "amorphous polyamide" as herein used refers to a polyamide that lacks in crystallinity, which has no endothermic crystalline melting peak when measured using a differential scanning calorimeter (DSC) ASTM D3417, 10°C/min.).

[40] In general, the polyamide can be prepared from a diamine and a dicarboxylic acid.

Examples of suitable diamines include hexamethylenediamine, 2-methylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)isopropylidene, 1 ,4-diaminocyclohexane, 1,3-diaminocyclohexane, meta-xylylenediamine, 1,5-diaminopentane, 1,4-diaminobutane, 1,3-diaminopropane, 2-ethyldiaminobutane, 1,4-diaminomethylcyclohexane, meta-xylylenediamine, alkyl-substituted or un- substituted m-phenylenediamine, and p-phenylenediamine. Examples of suitable dicarboxylic acids include alkyl-substituted or unsubstituted isophthalic acid, terephthalic acid, adipic acid, sebacic acid, and butanedicarboxylic acid.

[41] Polyamide prepared from an aliphatic diamine and an aliphatic dicarboxylic acid is general semi-crystalline polyamide (also referred to as 'crystalline nylon') and is not amorphous polyamide. Polyamide prepared from an aromatic diamine and an aromatic dicarboxylic acid is difficult to treat under common conditions for melting processes.

[42] Accordingly, amorphous polyamide can be prepared from either an aromatic diamine and an aliphatic dicarboxylic acid or an aromatic dicarboxylic acid and an aliphatic diamine. Aliphatic groups of the amorphous polyamide are preferably Cl -C 15 aliphatic groups or C4-C8 alicyclic alkyl groups. Aromatic groups of the amorphous polyamide are preferably substituted C1-C6 mono- or bicyclic aromatic groups. However, all types of the amorphous polyamide are not necessarily suitable for use in the present invention. For example, meta-xylylenediamine adipamide is readily crystallized under typical heating conditions for a thermal molding process or when being oriented, which is unfavorable.

[43] Specific examples of amorphous polyamides suitable for use in the present invention include hexamethylenediamine isophthalamide, a hexamethylenediamine isophthalamide/terephthalamide terpolymer having an isophthalic acid/terephthalic acid ratio of 99/1 to 60/40, a mixture of 2,2,4- and

2,4,4-trimethylhexamethylenediamine terephthalamide, and a copolymer of isophthalic acid, terephthalic acid or a mixture thereof with hexamethylenediamine or 2-methylpentamethylenediamine. Polyamide based on hexamethylenediamine isophthalamide/terephthalamide, which has a high terephthalic acid content, is also useful, but it must be mixed with another diamine, such as 2-methyldiaminopentane, in order to produce a processible amorphous polyamide. [44] The amorphous polyamide based on the above monomers only may contain a small amount of a lactam, such as caprolactam or lauryl lactam, as a co-monomer. Importantly, the polyamide is amorphous in its entirety. Therefore, any co-monomer can be used in the present invention so long as it does not make the polyamide crystalline. The amorphous polyamide may include about 10% by weight or less of a liquid or solid plasticizer, such as glycerol, sorbitol or toluenesulfonamide (Santicizer 8, Monsanto). In most applications, the Tg of the amorphous polyamide (as measured in a dry state, i.e. a state in which about 0.12% by weight or less of moisture is contained) must be within the range of about 70°C to about 170°C and preferably about 80°C to about 160°C. The amorphous polyamide, which is not specially blended, has a Tg of about 125°C in a dry state. The lower limit of the Tg of the amorphous polyamide is approximately 70°C, although it is not clear. The upper limit of the Tg of the amorphous polyamide is not clear, either. However, the use of the polyamide having a Tg of about 170°C or higher renders thermal molding of the final composition difficult. Therefore, polyamide having aromatic groups at both acid and amine moieties cannot be thermally molded because it has too high a Tg, which is not generally suitable for the objects of the present invention.

[45] The polyamide may also be semi-crystalline. The semi-crystalline polyamide is generally prepared using a lactam, such as nylon 6 or nylon 11, or an amino acid, or is prepared by condensing a diamine, such as hexamethylenediamine, with a dibasic acid, such as succinic acid, adipic acid or sebacic acid. The polyamide may be a copolymer or a terpolymer, for example, a copolymer {e.g., nylon 6, nylon 66) of hexam- ethylenediamine/adipic acid and caprolactam. A mixture of two or more crystalline polyamides may also be used. The semi-crystalline and amorphous polyamides are prepared by polycondensation processes well known in the art.

[46] The ionomer is preferably a copolymer of acrylic acid and ethylene, and has a melt index of 0.1 to 10 g/10 min (190°C, 2,16Og).

[47] The content of the nanocomposite having barrier properties in the nanocomposite composition is preferably 0.5 to 60 parts by weight and more preferably 3 to 30 parts by weight. The presence of the nanocomposite having barrier properties in an amount of less than 0.5 parts by weight leads to an insignificant improvement in barrier properties. Meanwhile, the presence of the nanocomposite having barrier properties in an amount greater than 60 parts by weight results in difficult processing.

[48] In the sealing system of the present invention, the compatibilizer functions to improve the compatibility of the polyolefin resin and the nanocomposite having barrier properties to form a composition with a stable structure.

[49] The compatibilizer may be a hydrocarbon polymer having a polar group. When a hydrocarbon polymer having a polar group is used, the hydrocarbon moiety, as a base of the polymer, increases the affinity of the compatibilizer for the polyolefin resin and for the nanocomposite having barrier properties, thereby making a final molded article stable in structure.

[50] As the compatibilizer, there can be used at least one copolymer selected from the group consisting of an epoxy-modified polystyrene copolymer, an ethylene-ethylene anhydride-acrylic acid copolymer, an ethylene-ethyl acrylate copolymer, an ethylene- alkyl acrylate-acrylic acid copolymer, maleic anhydride modified (graft) high-density polyethylene, maleic anhydride modified (graft) linear low-density polyethylene, an ethylene-alkyl methacrylate-methacrylic acid copolymer, an ethylene-butyl acrylate copolymer, an ethylene- vinyl acetate copolymer, a maleic anhydride modified (graft) ethylene- vinyl acetate copolymer, modified products thereof, and mixtures thereof.

[51] The content of the compatibilizer in the nanocomposite composition is preferably 1 to 30 parts by weight and more preferably 3 to 15 parts by weight. If the compatibilizer is present in an amount of less than 1 part by weight, the mechanical properties of a molded article manufactured from the nanocomposite composition are poor. If the compatibilizer is present in an amount exceeding 30 parts by weight, the molding processing of the composition undesirably becomes difficult.

[52] A preferred epoxy-modified polystyrene copolymer as the compatibilizer is a copolymer that is composed of a backbone, which contains 70 to 99 parts by weight of styrene and 1 to 30 parts by weight of an epoxy compound represented by Formula 1 below:

[53]

H H R C C R'

\ / O

(1) [54] wherein R and R' are each independently a C1-C20 aliphatic or C5-C20 aromatic residue having a double bond at the terminals of the molecular structure, and [55] branches, which contain 1 to 80 parts by weight of the acrylic monomer represented by Formula 2 below: [56] CH₂ CH

= O

CH₃ (2)

[57] Each of the maleic anhydride modified (graft) high-density polyethylene, maleic anhydride modified (graft) linear low-density polyethylene and maleic anhydride modified (graft) ethylene- vinyl acetate copolymer preferably is composed of 100 parts by weight of the backbone and 0.1 to 10 parts by weight of branches containing maleic anhydride. When maleic anhydride is present in an amount lower than 0.1 parts by weight, the performance of the compatibilizer is not satisfactorily exerted. Meanwhile, when maleic anhydride is present in an amount greater than 10 parts by weight, an unpleasant smell is undesirably produced during molding of the composition.

[58] The nanocomposite composition of the present invention is prepared by simultaneously adding the nanocomposite having barrier properties in a pellet form, the compatibilizer and the polyolefin resin in a given ratio to a pellet mixer, followed by dry blending.

[59] The dry-blended composition is melt-blended and molded in an extrusion molding machine to form a constituent layer of the plate. The molding may be performed by common molding processes, including blow molding, extrusion molding, pressure molding and injection molding.

[60] The plate is welded to the wall of the tank at the location of the periphery of the opening. The term "welding" means that the plate is made integral with the tank wall through the contact and partial interpenetration of the molecules of a portion of the surface of one of the two main sides of the plate juxtaposing the edges of the latter and forming a sealing surface in the form of a closed ring, a circular shape, or any shape and more or less precisely molded to the outer perimeter of this side of the plate, with the molecules of a similar surface of the tank, located on the edge of the opening, along its entire periphery.

[61] The plate may have a multilayer structure including a layer formed of the nanocomposite composition having barrier properties. In this case, it is possible to incorporate a nanocomposite composition having barrier properties into one of the layers of the plate or to insert a particular additional layer, essentially constituted by a nanocomposite composition having barrier properties, into the structure. Preferably, an additional layer essentially constituted by a nanocomposite composition having barrier properties is inserted into the structure. In the case where the plate has a multilayer structure, it is preferred that the external layer of the plate welded to the tank have a composition compatible with that of a layer constituting the external wall of the tank. The term "compatibility" means a chemical and physical compatibility of the constituents of the respective compositions of the layer of the plate welded to the tank and the external wall of the latter in the vicinity of the opening. Good compatibility prevents any phenomena of segregation of certain constituents of the respective compositions of the welded parts, as well as any chemical reaction or physical phenomenon detrimental to the properties of the tank whose opening is thus sealed. Good compatibility generally guarantees the long-term adhesion of the plate to the tank.

[62] The multilayer structure of the plate may be different from or identical to that of the walls of the tank itself. Sealing systems in which the structure of the plate is identical to that of the walls of the tank are often preferred. Most particularly preferred are systems in which, within identical structures, the nanocomposite compositions having barrier properties themselves are identical and constitute identical polymer layers.

[63] The expression "external layer of the plate" is understood to mean a layer whose one face is adjacent to another layer of the plate and whose other face is in contact with the environment external to this plate.

[64] The system according to the invention is quite suitable for sealing a simple opening of a tank. It is also suitable for sealing an opening that lies over an accessory located inside the tank.

[65] According to a particularly preferred embodiment of the sealing system according to the invention, the plate is integral with at least one accessory located on the internal surface of the tank. The term "accessory" indicates any element in general through which liquid or gas passes, or which is in contact with liquid or gas and fulfills a particular function specific to the device of which the tank is a part, including a function for transporting liquid and/or gas between two other elements.

[66] Non-limiting examples of such accessories include the following accessories:

[67] - A receptacle containing any chemical or physical composition, particularly a vapor absorption canister

[68] - A liquid or gas gauge

[69] - An electrical connection leading to a liquid or gas gauge

[70] - A liquid or gas pump

[71] - A safety valve for the controlled sealing of the tank in certain specific situations, for example, a roll-over valve (ROV), i.e. a valve that will automatically close in the event of the tank turning upside down

[72] - A drainable receptacle for collecting liquid

[73] - An electrical connection for supplying power to the motor of a liquid or gas pump

[74] - A liquid conduit leading to a device for feeding any device, especially a motor

[75] - A liquid-vapor separation device, for example, an on-board refueling vapor recovery (ORVR) valve, i.e. a device for vapor recovery when refueling the tank, or an on-board diagnostic (OBD) device.

[76] Any combination of at least two accessories can be used, possibly in the presence of several instances of the same accessory.

[77] According to this embodiment, the accessory is integral with the plate, i.e. it is joined to the plate by a mechanical means. The accessory is attached to the plate by any mechanical means that is compatible with the type of the tank, the nature of the liquid and the gas that is stored in it, and the normal use that is made of the tank. The plate can provide a means for grasping and transporting the accessory. It is possible, for example, to use a plate to which the accessory has been attached by a mechanical mounting device. Such devices include, for example, screws, nuts, clipping systems, etc. It is also possible to use a plate and an accessory that have been attached during their production, for example, by molding. It is also possible to use a more permanent means of attachment, such as adhesive bonding or welding. It is generally preferable for the accessories to be attached to the plate by welding.

[78] The accessory attached to the plate is disposed relative to the latter on the side of the plate that is inside the tank when it is sealed.

[79] Some of these accessories can include at least one pipe that passes through the plate via a hole cut into the latter. In this case, it is often advantageous to equip the opening through which the pipe exits with a seal.

[80] The plate can also be shaped so as to adapt as closely as possible to the environment of the opening to be sealed, as well as to the shape and the volume of the accessory to which it is attached. A plate attached to a liquid- vapor separator comprising a vapor escape conduit that passes through the plate via a hole has produced good results.

[81] The present invention also provides a method for sealing an opening of a tank, the method comprising the steps of: (a) dry-blending (i) 100 parts by weight of a polyolefin resin, (ii) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcoholand (iii) 1 to 30 parts by weight of a compatibilizer to prepare a nanocomposite composition having barrier properties; (b) producing a plate, which includes a layer formed of the nanocomposite composition, by molding; and (c) welding the plate to periphery of an opening of a tank to seal the opening.

[82] The plate used in this method can have various origins. It can, for example, be produced independently of the tank itself, at a different time or not, by means of a specific process that is not necessarily identical to that used to produce the tank. For example, the plate can be obtained by co-extrusion followed by compression molding. It can also be obtained by molding using one of many known techniques. Such techniques are, for example, blow molding, compression molding, injection molding and thermoforming.

[83] When the plate is produced independently of the tank, an opening in the tank is produced whose dimensions are slightly smaller than those of the tank, and the opening is subsequently sealed by the welding of the plate.

[84] In a variant, the plate can be produced simultaneously with the tank and cut from the plastic used to produce the tank. This way of working is especially advantageous from the point of view of synchronizing the production of tanks equipped with their accessories. It is possible, for example, to cut the plate directly from a region of the wall of the tank after the production of the latter, or from a part of the latter. This variant also assumes that the innermost external layer of the multilayer structure of the tank is compatible with its outermost layer.

[85] Another variant is to cut the plate from the scraps of the tank production, as long as they have the appropriate multilayer structure.

[86] It is also possible to cut the plate from an extension of the tank specially designed for this purpose and produced simultaneously with the latter. Lastly, it is also possible to produce plates comprising two complete structures identical to that of the walls of the tank, by compressing two structures identical to the wall of the tank. In this case, it is possible, for example, to compress a particular part of the parison used to produce the tank. In doing this, it is especially advantageous to compress two identical structures of the plate against the mold for producing the tank.

[87] The operation for welding the plate to the tank can be done using any generally known technique by itself. It is possible, for example, to use hot-plate welding, vibration welding or laser welding technique. The hot-plate welding technique is preferred.

[88] According to a particular embodiment of the method according to the invention, at least one accessory is attached to the plate, on the side inside the tank. Any method of attachment that is compatible with the tank, the nature of the liquid and the gas it contains, and the conditions of its use is generally suitable.

[89] It is preferable, however, to use a welding method to perform this attachment.

[90] Here again, the term "attachment" and the expression "side inside the tank" have the same meanings as already explained above in the case of the sealing system.

[91] In this particular embodiment of the method according to the invention, a first variant consists of welding at least one accessory to the plate before sealing the opening of the tank by welding the plate attached to the accessory to the periphery of this opening.

[92] In this way, the plate plays the role of supporting the accessory and allows it to be easily inserted into the tank.

[93] By contrast, a second variant consists of attaching, in a first step, at least one accessory to the inner wall of the tank adjacent to the opening, and in a second subsequent step, of sealing the tank by welding the plate simultaneously to the accessory and to the periphery of the opening.

[94] Whichever embodiment of the method is used, a problem may arise during the operation for welding the plate to the wall of the tank when the latter, for any reason, experiences a flexible deformation in the vicinity of the opening, for example, under the influence of its own weight or as a result of forces exerted perpendicular to the surface of the tank during the welding. Such a situation may actually occur when the tank has come directly from production and the temperature of its walls is still relatively high. Another reason could be that the diameter of the opening is relatively large and the plastic material in the vicinity of the edge of the opening is not supported as effectively as in the case of small openings. The invention also relates to a sealing method that remedies these problems of flexible deformation of the tank wall, by supporting the tank wall in the vicinity of the opening during welding of the plate by means of lugs molded to this wall. The lugs may be molded to the external wall of the tank in the vicinity of the periphery of the opening. The wall of the tank is supported in this location by means of clamps that clamp onto the lugs. Lugs similar to those described above can also be used while the plate is cut from the wall of the tank, in order to prevent the deformation of the latter. The lugs can also be used to correct, prior to the welding operation, any unevenness that may occur on the surface of the tank. Lastly, they can also contribute to making the shape of the external surface of the tank correspond perfectly to that of the plate.

[95] The invention also concerns the use of the method described above to seal an opening of a fuel tank, particularly for a motor vehicle.

[96] The term "motor vehicle" is understood to mean vehicles powered by an internal- combustion engine, such as lorries, cars and motorcycles.

[97] Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

[98] FlG. 1 is a cross-sectional view of a tank sealed by the sealing system of the present invention.

[99] A tank 10 has a monolayer structure in which an opening is sealed by a plate 6 carrying two accessories, and is formed of the nanocomposite composition having barrier properties. According to the monolayer structure of a wall 2 of the tank 10, a siphon 1 is snap-fastened onto a rim 3 of the wall 2 of the tank 10. A venting ROV valve 5 having a float 4 and provided with a polyacetal skirt is again fixed to the siphon 1 by snap-fastening.

[100] The plate 6 having a monolayer formed of the nanocomposite composition having barrier properties is molded by thermal molding so that peripheral regions 7, 8 and 11 are slimmed down. The plate 1 is welded to the outer surface of the tank by hot-plate welding.

[101] As a variant, the multilayer structure of the plate may also comprise two different barrier layers. A preferred example according to this variant is that of plates having two complete structures identical to that of the walls of the tank, stacked one on top of the other and resulting from the compression of two structures identical to the walls of the tank. Another variant consists in producing, near the edge of the plate, an embossment in which the thicknesses of the layers are reduced, in particular those of the layers other than the barrier layer. The benefit is in this case to further limit the risk of loss by transmission at the point where the plate is welded to the tank.

[102] According to a preferred way of implementing the method according to the invention, a composition opaque to the laser radiation or to the infrared radiation is incorporated into the plastic layer of the slimmed-down region in contact with the outer surface of the tank. Advantageously, this method of implementation produces tanks in which the welding by laser or infrared radiation of the slimmed-down peripheral region of the plate is of better quality. The expression "composition opaque to laser or infrared radiation" is understood to mean a composition that absorbs and/or reflects a substantial proportion of the laser or infrared radiation energy. An example of such a composition that has given good results is a carbon black filler. This composition is advantageously distributed uniformly throughout the polymeric material of the layer directly in contact with the wall of the tank.

[103] Hereinafter, the present invention will be explained in more detail with reference to the following examples. However, these examples are given for the purpose of illustration and are not intended to limit the present invention.

[104]

[105] EXAMPLES

[106] Materials used in the following examples are as follows:

[107] - EVOH: E105B, Kuraray, Japan

[108] - Nylon 6: EN 500, KP Chemicals, Korea

[109] - Ionomer: SURLYN 8527, Dupont, USA

[110] - HDPE-g-MAH: Compatibilizer, PB3009, CRAMPTON

[111] - HMWPE: High-molecular weight polyethylene resin, PB 150, LG Daesan

Petrochemical Ltd., Korea

[112] - Clay: Cloisite 2OA, SCP

[113] - Heat stabilizer: IR 1098, Songwon Industrial Co., Ltd., Korea

[114] - Adhesive: AB 130, LG Chem., Korea

[115]

[116] [Preparative Example 1] Preparation of EVOH-layered clay nanocomposite

[117] 97 wt% of an ethylene- vinyl alcohol copolymer (EVOH) (E- 105B (ethylene content: 44 mol%), Kuraray, Japan; melt index: 5.5 g/10 min., density: 1.14 g/cm3) was introduced into a main hopper of a co-rotating twin screw extruder (Φ40) (SM Platek Co., Ltd., Korea). Then, 3.0 wt% of organically modified montmorillonite (Cloisite 2OA, Southern Clay Products, USA) as a layered clay, and 0.1 parts by weight of a heat stabilizer (IR 1098) based on a total of 100 parts by weight of the EVOH and the organically modified montmorillonite were separately introduced into a side feeder of the twin-screw extruder to prepare an EVOH/layered clay nanocomposite in a pellet form. Extrusion was carried out under the following conditions: extrusion temperature of 180-190-200-200-200-200-200°C, screw rotation speed of 300 rpm, and discharge rate of 30 kg/hr.

[118]

[119] [Preparative Example 2] Preparation of nylon 6-layered clay nanocomposite

[120] 97 wt% of polyamide (nylon 6, EN300) was introduced into a main hopper of a co- rotating twin screw extruder (Φ40) (SM Platek Co., Ltd., Korea). Then, 3.0 wt% of organically modified montmorillonite as a layered clay, and 0.1 parts by weight of a heat stabilizer (IR 1098) based on a total of 100 parts by weight of the polyamide and the organically modified montmorillonite were separately introduced into a side feeder of the twin-screw extruder to prepare a polyamide/layered clay nanocomposite in a pellet form. Extrusion was carried out under the following conditions: extrusion temperature of 220-225-245-245-245-245-245°C, screw rotation speed of 300 rpm, and discharge rate of 40 kg/hr.

[121]

[122] [Preparative Example 3] Preparation of ionomer-layered clay nanocomposite

[123] 97 wt% of an ionomer was introduced into a main hopper of a co-rotating twin screw extruder (Φ40) (SM Platek Co., Ltd., Korea). Then, 3.0 wt% of organically modified montmorillonite as a layered clay, and 0.1 parts by weight of a heat stabilizer (IR 1098) based on a total of 100 parts by weight of the ionomer and the organically modified montmorillonite were separately introduced into a side feeder of the twin- screw extruder to prepare an ionomer/layered clay nanocomposite in a pellet form. Extrusion was carried out under the following conditions: extrusion temperature of 220-225-245-245-245-245-245°C, screw rotation speed of 300 rpm, and discharge rate of 40 kg/hr.

[124]

[125] [Example 1]

[126] 25 parts by weight of the EVOH nanocomposite prepared in Preparative Example

1, 5 parts by weight of a compatibilizer and 70 parts by weight of high-density polyethylene were introduced into a dry blender (Double cone mixer, MYDCM-100, Myeong Woo Micron System, Korea). After the mixture was dry-blended for 30 minutes, the blend was introduced into a main hopper of a blow molding machine and blow-molded at extrusion temperatures of 185-195-195-195°C to produce a fuel tank having a volume of 70 liters (weight: 6 kg). A plate was obtained from the scraps of the tank production. The plate was cut from an extension of the tank produced simultaneously with the tank. Therefore, the plate had the same composition as that of the fuel tank.

[127]

[128] [Example 2]

[129] 25 parts by weight of the nylon 6 nanocomposite prepared in Preparative Example

2, 5 parts by weight of a compatibilizer and 70 parts by weight of high-density polyethylene were introduced into a dry blender (Double cone mixer, MYDCM-100, Myeong Woo Micron System, Korea) using a tumble mixer. After the mixture was dry-blended for 30 minutes, the blend was introduced into a main hopper of a blow molding machine and blow-molded at extrusion temperatures of 195-210-220-220°C to produce a fuel tank having a volume of 70 liters (weight: 6 kg). A plate was obtained from the scraps of the tank production. The plate was cut from an extension of the tank produced simultaneously with the tank. Therefore, the plate had the same composition as that of the fuel tank.

[130]

[131] [Example 3]

[132] 5 parts by weight of the nylon 6 nanocomposite prepared in Preparative Example 2,

2 parts by weight of a compatibilizer and 93 parts by weight of high-density polyethylene were introduced into a dry blender (Double cone mixer, MYDCM-100, Myeong Woo Micron System, Korea). After the mixture was dry-blended for 30 minutes, the blend was introduced into a main hopper of a blow molding machine and blow-molded at extrusion temperatures of 195-210-220-220°C to produce a fuel tank having a volume of 70 liters (weight: 6 kg). A plate was obtained from the scraps of the tank production. The plate was cut from an extension of the tank produced simultaneously with the tank. Therefore, the plate had the same composition as that of the fuel tank.

[133]

[134] [Example 4]

[135] 40 parts by weight of the nylon 6 nanocomposite prepared in Preparative Example

2, 20 parts by weight of a compatibilizer and 40 parts by weight of high-density polyethylene were introduced into a dry blender (Double cone mixer, MYDCM-100, Myeong Woo Micron System, Korea). After the mixture was dry-blended for 30 minutes, the blend was introduced into a main hopper of a blow molding machine and blow-molded at extrusion temperatures of 195-210-220-220°C to produce a fuel tank having a volume of 70 liters (weight: 6 kg). A plate was obtained from the scraps of the tank production. The plate was cut from an extension of the tank produced simultaneously with the tank. Therefore, the plate had the same composition as that of the fuel tank.

[136] [137] [Example 5]

[138] 25 parts by weight of the ionomer nanocomposite prepared in Preparative Example

3, 5 parts by weight of a compatibilizer and 70 parts by weight of high-density polyethylene were introduced into a dry blender (Double cone mixer, MYDCM-100, Myeong Woo Micron System, Korea). After the mixture was dry-blended for 30 minutes, the blend was introduced into a main hopper of a blow molding machine and blow-molded at extrusion temperatures of 240-265-265-265°C to produce a fuel tank having a volume of 70 liters (weight: 6 kg). A plate was obtained from the scraps of the tank production. The plate was cut from an extension of the tank produced simultaneously with the tank. Therefore, the plate had the same composition as that of the fuel tank.

[139]

[140] [Comparative Example 1]

[141] HMWPE, a first adhesive, EVOH, a second adhesive, and HMWPE were introduced in this order into a blow molding machine equipped with five extruders, followed by blow molding to produce a fuel tank (volume: 70 liters (weight: 6 kg)) having a HMWPE/first adhesive/EVOH/second adhesive/HMWPE structure. A plate was obtained from the scraps of the tank production. The plate was cut from an extension of the tank produced simultaneously with the tank. Therefore, the plate had the same composition as that of the fuel tank.

[142]

[143] [Test for Barrier Properties]

[144] Each of the fuel tanks produced in Examples 1 to 5 and Comparative Example 1 was filled with 30 kg of fuel. C (toluene 50% + iso-octane 50%). The openings of the fuel tanks produced in Examples 1 to 5 and Comparative Example 1 were sealed using the respective plates produced in Examples 1 to 5 and Comparative Example 1 by hotplate welding. The resulting structures were put in a large-sized oven. After the structures were allowed to stand in the oven at 40°C for 30 days, their initial weight (Wo) was measured. 200 days after the charging, the structures were taken out from the oven and weighed (Wl). A loss in weight (Wo-Wl) was calculated by subtracting the weight (Wl) from the initial weight (Wo).

[145] <TABLE 1>

[146] Test results for fuel-barrier properties

[147] Example No. Loss in weight

Example 1 10.3

Example 2 15.3

Example 3 14.9

Example 4 12.3

Example 5 17.1

Comparative Exarrple ' 19.2

[148] As can be seen from the data shown in Table 1, the sealing systems manufactured in Examples 1 to 5 showed superior fuel-barrier properties, compared to the sealing system manufactured in Comparative Example 1. Industrial Applicability

[149] As apparent from the above description, the system for sealing an opening of a tank according to the present invention can reduce the losses of liquid and gas when compared to known sealing systems and makes it possible to achieve loss levels low enough to meet the new environmental standards that are programmed to come into force in the near future both in Europe and the United States. According to the sealing system of the present invention, a tank is produced using a nanocomposite composition having superior barrier properties, and at the same time, an opening of the tank is sealed using a plate made of a nanocomposite composition having barrier properties. As a result, the sealing system of the present invention can maintain its inhibitory functions on the penetration and permeation of tank contents even after a long time of use, has excellent mechanical strength, shows superior oxygen-barrier properties, organic solvent-barrier properties and moisture-barrier properties, and enables a nanocomposite to maintain exfoliated morphology thereof, in which the nanocomposite is dispersed in a specific form in a polymer matrix, even after completion of molding processes.

[150] In light of the above teachings, various practices and modifications of the present invention can be readily made without departing from the scope and spirit of the invention by those skilled in the art.

Claims

[1] A system for sealing an opening of a tank, the system comprising a plate welded to a wall of a tank at the location of the periphery of an opening of the tank wherein the plate includes a layer formed of a nanocomposite composition having barrier properties, the nanocomposite composition being prepared by dry- blending (a) 100 parts by weight of a polyolefin resin, (b) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcohol,and (c) 1 to 30 parts by weight of a compatibilizer.

[2] The system according to claim 1, wherein the resin having barrier properties and the layered clay are present in a weight ratio ranging from 58.0: 42.0 to 99.9: 0.1 in the nanocomposite having barrier properties.

[3] The system according to claim 1, wherein the layered clay is one or more selected from the group consisting of montmorillonite, bentonite, kaolinite, mica, hectorite, fluorohectorite, saponite, beidellite, nontronite, stevensite, vermiculite, hallosite, volkonskoite, suconite, magadite, and kenyalite.

[4] The system according to claim 1, wherein the layered clay in the nanocomposite having barrier properties contains 1 to 45% by weight of an organic modifier therein.

[5] The system according to claim 4, wherein the organic modifier is an organic material having a functional group selected from the group consisting of primary ammonium, secondary ammonium, tertiary ammonium, quaternary ammonium, phosphonium, maleate, succinate, acrylate, benzylic hydrogen, oxazoline, and distearyldimethylammonium groups.

[6] The system according to claim 1, wherein the ethylene- vinyl alcohol copolymer has an ethylene content of 10 to 50 mol%.

[7] The system according to claim 1, wherein the polyamide is selected from 1) nylon 46, 2) nylon 6, 3) nylon 66, 4) nylon 610, 5) nylon 7, 6) nylon 8, 7) nylon 9, 8) nylon 11, 9) nylon 12, 10) nylon 46, 11) MXD6, 12) amorphous polyamide, 13) a polyamide copolymer containing two or more polyamides of the polyamides 1) to 12), and 14) mixtures of two or more polyamides of the polyamides 1) to 12).

[8] The system according to claim 7, wherein the amorphous polyamide has a glass transition temperature (Tg) of about 80°C to about 130°C.

[9] The system according to claim 7, wherein the amorphous polyamide is selected from the group consisting of hexamethylenediamine isophthalamide, a hexam- ethylenediamine isophthalamide/terephthalamide terpolymer having an isophthalic acid/terephthalic acid ratio of 99/1 to 60/40, a mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine terephthalamide, and a copolymer of isophthalic acid, terephthalic acid or a mixture thereof with hexam- ethylenediamine or 2-methylpentamethylenediamine.

[10] The system according to claim 9, wherein the amorphous polyamide is a hexam- ethylenediamine isophthalamide/terephthalamide terpolymer having an isophthalic acid/terephthalic acid ratio of about 70/30.

[11] The system according to claim 1, wherein the ionomer has a melt index ranging from 0.1 to 10 g/10 min (190°C, 2,160 g).

[12] The system according to claim 1, wherein the compatibilizer is at least one copolymer selected from the group consisting of an ethylene-ethylene anhydride- acrylic acid copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-alkyl acrylate-acrylic acid copolymer, maleic anhydride modified (graft) high-density polyethylene, maleic anhydride modified (graft) linear low-density polyethylene, an ethylene-alkyl methacrylate-methacrylic acid copolymer, an ethylene-butyl acrylate copolymer, an ethylene- vinyl acetate copolymer, and a maleic anhydride modified (graft) ethylene- vinyl acetate copolymer.

[13] The system according to claim 1, wherein the plate is attached to at least one accessory positioned inside the tank.

[14] The system according to claim 1, wherein the plate has a monolayer or multilayer structure.

[15] A method for sealing an opening of a tank, the method comprising the steps of:

(a) dry-blending (i) 100 parts by weight of a polyolefin resin, (ii) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcoholand (iii) 1 to 30 parts by weight of a compatibilizer to prepare a nanocomposite composition having barrier properties;

(b) producing a plate, which includes a layer formed of the nanocomposite composition, by molding; and

(c) welding the plate to periphery of an opening of a tank to seal the opening. [16] The composition according to claim 15, wherein the molding is performed by blow molding, extrusion molding, pressure molding, or injection molding. [17] The composition according to claim 15, wherein the tank includes a layer formed by dry-blending (i) 100 parts by weight of a polyolefin resin, (ii) 0.5 to 60 parts by weight of a nanocomposite having barrier properties composed of a layered clay andat least one resin having barrier properties selected from the group consisting of an ethylene- vinyl alcohol copolymer, polyamide, an ionomer and polyvinyl alcohol,and (iii) 1 to 30 parts by weight of a compatibilizer. [18] The composition according to claim 15, wherein the plate is welded to the opening of the tank by hot-plate welding, vibration welding, or laser welding.