HK1058158B - Process for improving interfacial adhesion in a laminate - Google Patents

Description

Method for improving interfacial bonding of laminates

Technical Field

The present invention relates to a method of manufacturing a laminate, in particular a laminate having a layer comprising a thermoplastic elastomer adjacent to a layer comprising a polymeric barrier material.

Background

Laminated barrier membranes and inflatable bladders formed from such membranes have been used in many products for inflation or cushioning, including automobile tires, balls, reservoirs used on heavy machinery, and on footwear. It is often desirable to form the film from thermoplastic polymeric materials because thermoplastic materials can be recycled and reformed into new articles, thereby reducing waste during manufacturing operations and facilitating recycling of the articles after use. Thermoplastic barrier films can be flexed to some extent due to thinness, but thermoplastic barrier films having only a layer of barrier material generally do not have sufficient elasticity for many applications, particularly for applications in which the inflated bladder is subjected to high strains in use. To overcome this problem, release materials have been blended or laminated with elastomeric materials. After removal of the deforming force, the resilient material or elastomer may substantially recover their original shape and size even when the part undergoes significant deformation.

However, bladder barrier films known as composites or laminates can also present a number of problems in footwear bladders and other bladders that are subject to high strain. In particular such airbag laminates may undergo layer separation and peeling. When such a force is applied to the pressurized bladder, deformation of the bladder will create a shear force at the interface of the laminate layers. Repeated deformation will fatigue the interface, leading to interlayer separation. Delamination is particularly severe if there are seams in the construction. Therefore, interfacial peel adhesion strength is a very important property for forming pressurized bladders that can withstand high strains in use.

In preparing the multilayer laminate, some previously known multilayer airbags employ tie layers or adhesives to achieve a sufficiently high interlayer bond strength to avoid delamination problems. However, the use of such tie layers or adhesives generally prevents any waste generated during product formation from being reground and recycled into useful products, thereby making production more expensive and generating more waste. The use of adhesives also adds to the expense and complexity of preparing laminates. These and other perceived shortcomings of the prior art are described in more detail in U.S. Pat. Nos. 4340626, 4936029, and 5042176 to Rudy, which are hereby incorporated by reference.

Other methods are to react the two different materials together to form a layer of graft copolymer or graft copolymer at the interface of the layers of the two different materials. Moureaux, U.S. patent 5036110, is an example of a graft copolymer composition and is incorporated herein by reference. Moureaux discloses an elastomeric membrane for a gas-water accumulator comprising a film of a thermoplastic polyurethane graft copolymer and an ethylene vinyl alcohol copolymer.

In another approach, a film laminate is described that excludes adhesive tie layers by providing a film comprising a first layer of a thermoplastic elastomer (e.g., a thermoplastic polyurethane) and a second layer comprising a barrier material (e.g., a copolymer of ethylene and vinyl alcohol), wherein hydrogen bonding occurs on the film segment between the first layer and the second layer. Laminates having a layer of flexible material and a layer of fluid barrier material are described, for example, in U.S. patent 6082025, granted 7/4/2000, U.S. patent 6013340, granted 1/11/2000, U.S. patent 5952065, granted 9/14/1999, and U.S. patent 5713141, granted 2/3/1998, which are incorporated herein by reference. While the films disclosed in these references provide flexible, "permanently" inflated, gas-filled shoe cushioning elements, which are believed to provide significant improvements in the art, the present invention still provides further improvements, particularly in terms of improved interface bonding.

Summary of The Invention

The present invention provides a method of improving the interfacial bonding between two adjacent thermoplastic layers of a laminate membrane. The method includes at least one annealing the laminate membrane by heating the laminate membrane to a temperature above the thermal transition temperature of at least one polymeric component of one or both layers for a time sufficient for partial diffusion of the at least one component through the boundary into the adjacent layer. By "partially diffuse across the interfacial boundary into an adjacent layer" is meant that a detectable amount of the component diffuses into the adjacent layer. Diffusion through the interfacial boundary can be measured indirectly as an increase in the peel strength of the film layer. Peel strength can be measured by ASTM D1876T-peel test (correct knowledge, finishing is not necessary because no adhesive is used). In a preferred embodiment, the peel strength can be increased by at least 100%, more preferably at least 500%, over that obtained without the process of the invention.

The method may further include the step of forming the laminate from the molten material and may also include shaping the laminate with heat prior to the annealing step. When the laminate is at a temperature below that at which significant diffusion through the interface boundary occurs, there may be a period of time, referred to herein as "lag time", between the steps of forming and shaping the laminate and the annealing step. In addition, the annealing step may be performed immediately after the step of forming the laminate.

The present invention also provides a laminate in which at least one component of at least one layer has partially diffused into an adjacent layer. In particular, the laminate membrane of the present invention may have an interfacial bond strength of at least about 20 lbs/linear inch. The thermoplastic elastomer layer as one of the adjacent layers provides elasticity to the laminate membrane of the present invention, while the barrier layer as the other adjacent layer allows the membrane to block the passage of fluid from one side of the membrane to the other. The durable elastic barrier film can be used to prepare an inflatable bladder. By "durable" is meant that the film has excellent resistance to fatigue failure, which means that the film can withstand repeated flexing and/or deformation and recovery without delamination along the film's layer interface, preferably over a wide temperature range. For the purposes of the present invention, the term "membrane" preferably refers to a free-standing thin film that separates a gas from another fluid (liquid or gas), preferably at a pressure higher than atmospheric pressure, or from said gas at a pressure lower than atmospheric pressure. Films laminated or coated onto another article for the purpose of non-separating fluids preferably do not fall within the definition of the inventive film.

The sealed, inflated airbag of the present invention made from the laminate film can be subjected to high strains without causing separation or peeling of the layers of the laminate layer, even at the seams. The present invention further provides enclosures (enclosures) including, but not limited to, permanently sealed inflatable bladders formed from the laminates of the present invention, and articles of manufacture comprising the enclosures and bladders. The bladder may be inflated with a gas such as nitrogen, air, super gas, and may be used to de-inflate or cushion, for example, a sport ball or footwear. The term "supergas" refers to a macromolecular gas, such as SF₆、CF₄、C₂F₆、C₃F₈And the like, as described in U.S. patent 4183156 to Rudy et al, 4287250 to Rudy, and 4340626 to Rudy, which are incorporated herein by reference. The barrier film preferably has a sufficiently low gas permeability to maintain the bladder "permanently" inflated, i.e., to maintain an internal pressure useful for the useful life of the article into which the bladder is incorporated. One acceptable method for measuring the relative permeability, and diffusion of different film materials is ASTM D-1434. The gas permeability of a membrane is expressed in terms of the amount of gas that diffuses through the membrane per unit area of time. The gas permeability can be represented by the unit cc/(m)²) (24 hours).

Detailed Description

The present invention provides a method comprising at least one step of annealing the laminate membrane by heating the laminate membrane to a temperature above the thermal transition temperature of at least one polymeric component of one layer or at least one polymeric component of each adjacent layer. The laminate membrane is annealed for a time sufficient to allow at least one component to diffuse through the boundary portion into the adjacent layer. "thermal transition temperature" refers to the midpoint of the temperature transition region beyond which a significant change in the properties of the polymeric component occurs. The thermal transition temperature may be a glass transition temperature or a crystalline melting temperature. Such thermal conversions are well known and described in the literature. The thermal transition temperature of a particular polymeric component can be determined experimentally by reference or by any known method, including differential scanning calorimetry, differential thermal analysis, thermogravimetric analysis, dynamic mechanical analysis, and the like.

Preferably, the annealing temperature is at least about 50 ℃ higher, more preferably at least about 80 ℃ higher, than the thermal transition temperature of at least one polymeric component of one or both layers. Temperatures higher than the annealing temperature required to obtain optimum interfacial bonding can be reduced for a short time, but should be below the flow temperature of the layer material to avoid deformation of the laminate membrane.

The laminate membrane is held at the annealing temperature for a time sufficient to allow partial diffusion of at least one component into an adjacent layer. Diffusion across the interface boundary can be observed by scanning electron microscopy or other means, and can also be conveniently measured indirectly as an increase in the peel strength of the film layer. Peel strength can be measured by ASTM D1876T-peel test (with proper knowledge that no finish is necessary because no adhesive is used). In preferred embodiments, the peel strength is at least about 100% higher, more preferably at least about 200% higher, than the peel strength obtained without the process of the present invention. In a more preferred embodiment, the peel strength is increased by at least a factor of about 5 over that obtained without the annealing process.

The laminate membrane should be exposed to the annealing temperature for at least about 1 minute, preferably at least about 5 minutes, more preferably at least about 15 minutes, and still more preferably at least about 20 minutes. In a highly preferred embodiment, the laminate membrane is exposed to the annealing temperature for at least about 30 minutes, and particularly at least about 40 minutes. The time that the laminate membrane is exposed to the annealing temperature can be quite long, but more than about 2 hours is economically less preferred. Furthermore, when the annealing temperature is sufficiently high to risk deformation of the laminate membrane with prolonged exposure time, the exposure time must be correspondingly shortened. Generally, the laminate membrane may be held at the annealing temperature for about 1 minute to about 2 hours, preferably about 5 minutes to about 90 minutes, and more preferably about 20 minutes to 1 hour. The annealing time and temperature required to achieve the desired result or maximum interlayer bonding can be determined by direct experimentation and will depend on factors apparent to those skilled in the art such as the thickness of each layer, the total thickness of the laminate membrane, and the specific composition of the layers. Generally, thicker layers, thicker laminates, and higher molecular weight components require longer times and higher temperatures. Generally, higher temperatures than the thermal transition temperature, thinner layers, and lower molecular weight components shorten the time necessary for annealing.

As an initial condition for at least one component to diffuse partially through the boundary into an adjacent layer, the surface tensions of the polymer melts forming the laminate film layers should be sufficiently close to wet the interface and adhere the adjacent layers. Preferably, the polymers or polymer blends used to prepare the film layers of the laminate are selected such that the difference in surface tension between the polymer melts is no more than about 1.5 dynes/cm²Still more preferably, the difference in surface tension between the two polymer melts is no more than about 1 dyne/cm². In addition, the closer the solubility parameter or polarity of the diffusing component is to that of the adjacent layer material, the more readily the component diffuses into the adjacent layer.

In a preferred embodiment, the laminate membrane includes as adjacent layers a thermoplastic elastomer layer and a thermoplastic gas barrier polymer layer. The thermoplastic elastomer layer typically comprises an amorphous polymeric component having a glass transition temperature, while the thermoplastic gas barrier polymer layer typically comprises a semi-crystalline polymeric component having a crystalline melt thermal transition associated with crystalline regions and a glass transition temperature associated with amorphous regions. The polymeric component that diffuses into the adjacent layer may be a polymer or may be a block unit of a block copolymer or a graft segment of a graft copolymer, such as a soft segment of a thermoplastic elastomer or a segment of a barrier copolymer material.

The thermoplastic elastomer layer comprises at least one thermoplastic elastomer material. Thermoplastic elastomers typically have soft or flexible segments or segments that provide elastomeric properties and hard or rigid segments that act as thermally reversible physical crosslinks, thereby allowing the polymer to be processed as a thermoplastic that retains elastic behavior at room temperature. For example, a thermoplastic elastomer has one or more soft or rubbery polymeric segments (e.g., polyester or polyether segments) and a hard or glassy polymeric segment (e.g., polyurethane or polyurea segments). A-B-A block copolymers such as styrene/butadiene/styrene block copolymers have a similar structure and due to the polymerization process the center of the polymer chain is always a soft or elastic segment (e.g., rubbery polybutadiene) while the ends are glassy (e.g., polystyrene). Other suitable classes of thermoplastic elastomers are dynamic vulcanizates, in which the rubber phase is vulcanized under shear in a molten thermoplastic phase.

Specific examples of useful thermoplastic elastomers include, but are not limited to, polyurethane-based elastomers prepared from polymeric polyols, including polyurethanes prepared from polyesters, polyethers, and polycarbonate diols (including polycaprolactone diols, polytetrahydrofuran diols, and polyester diols prepared from diols having 8 or more carbon atoms and dicarboxylic acids having 8 or more carbon atoms); a flexible polyolefin; styrene-based thermoplastic elastomers; a polyamide elastomer; polyamide-ether elastomers; a polymeric ester-ether elastomer; a flexible ionomer; thermoplastic vulcanizates such as EPDM vulcanized in polypropylene; flexible polyvinyl chloride homopolymers and copolymers; a flexible acrylic polymer; and combinations of these materials. Commercial materials include, but are not limited to, polyamide-ether elastomers sold by elf atochem under the trade name PEBAX *, ester-ether elastomers sold by DuPont under the trade name HYTREL *, ester-ester and ester-ether elastomers sold by DSM Engineering under the trade name ARNITEL *, thermoplastic vulcanizates sold by advanced elastomer Systems under the trade name SANTOPRENE *, elastomeric polyamides sold by emer under the trade name giamid *, elastomeric polyurethanes sold by dow chemical Company, Midland, MI under the trade name pellettane *, elastallan * polyurethanes sold by BASF Corporation, mt.olive, NJ, TEXIN * and DESMOPAN * polyurethanes sold by Bayer, Morton * polyurethanes sold by Morton, and esgosine * sold by b.f.

In one embodiment, the thermoplastic elastomer includes a polyurethane elastomer prepared with a polyester polyol or a polyether polyol, particularly a polyester polyol. The preparation of the above polyurethane elastomers is described in detail in U.S. patent 6082025, 7/4/2000, 6013340, 1/11/2000, 5952065, 9/14/1999, and 5713141, 2/3/1998, which are incorporated herein by reference. Preferred polyester polyols for use in the synthesis of polyurethane elastomers have glass transition temperatures of at least about-100 ℃, preferably at least about-50 ℃, more preferably at least about-30 ℃, and even more preferably at least about-20 ℃. Preferred polyester polyols have glass transition temperatures of up to about 30 ℃, preferably up to about 10 ℃, more preferably up to about-10 ℃. Particularly preferred polyester polyols have a glass transition temperature of from about-50 ℃ to about-10 ℃. The polyester polyols preferably have a weight average molecular weight of from about 500 to about 10,000, and a weight average molecular weight of at least about 650, more preferably at least about 1000, and up to about 5000, more preferably up to about 4000, and even more preferably up to about 2000. The preparation of polyester polyols is well known and suitable reactants are described in the above patents. The polyester diol preferably has a number average molecular weight of at least about 300, more preferably at least about 500, and even more preferably at least about 750. The polyester diol has a number average molecular weight of up to about 5000, more preferably up to about 2000, and even more preferably up to about 1500. In a preferred embodiment, the polyester diols have a number average molecular weight of from about 300 to about 5000, more preferably from about 500 to about 2000, and even more preferably from about 750 to about 2000. The number average molecular weight and the weight average molecular weight can be determined by, for example, ASTM D-4274.

Preferred polyester polyols include, but are not limited to, the hydroxy-functional reaction products of one or more dicarboxylic acids or dicarboxylic anhydrides, preferably aliphatic, having up to about 36 carbon atoms, preferably from about 2 to about 8 carbon atoms, and diols, preferably aliphatic diols, having from about 2 to about 12 carbon atoms, preferably from about 2 to about 8 carbon atoms, and the polymerization products of lactones such as gamma-butyrolactone, 6-valerolactone epsilon-caprolactone and/or hydroxycarboxylic acids. The preferred polymeric polyols are diols. Small amounts of mono-functional, tri-functional and higher functionality materials (possibly up to 5 mole%) may be included. Specific examples of suitable diols include, but are not limited to, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 6-hexanediol, 1, 3-butanediol, 2, 3-butanediol, 1, 3-pentanediol, 2, 3-pentanediol, neopentyl glycol, 1, 3-cyclopentanediol, 1, 4-cyclohexanediol, 3-dimethyl-1, 2-butanediol, 2-ethyl-2-methyl-1, 3-propanediol, 2-methyl-2, 4-pentanediol, 5-hexene-1, 2-diol, 2-propyl-1, 3-propanediol, pinacol, and the like, as well as combinations of these. A small amount of higher functionality polyol such as trimethylolpropane or glycerol may be used, preferably less than about 5% by weight polyol, more preferably less than about 2% polyol reactant. In a particularly preferred embodiment, the polyester is linear, i.e., employing only diols.

Suitable dicarboxylic acids and anhydrides include, but are not limited to, oxalic acid, malonic acid, glyoxylic acid, maleic acid, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, mesaconic acid, succinic acid, methylsuccinic acid, muconic acid, glutaric acid, adipic acid, pimelic acid, dimethylsuccinic acid, methylglutaric acid, cyclopentanedicarboxylic acid, butylmalonic acid, diethylmalonic acid, dimethylglutaric acid, methyladipic acid, ethylmethylsuccinic acid, and anhydrides thereof, and combinations of these acids and anhydrides. Preferred dicarboxylic acids include glutaric acid, succinic acid, malonic acid, maleic acid, adipic acid, and anhydrides thereof, and combinations of these acids and anhydrides.

In a preferred embodiment, the polyester is a polyester diol selected from polycaprolactone polyesters based on the reaction of epsilon-caprolactone with an initial diol such as ethylene glycol and a combination of polyesters prepared from the reaction of ethylene glycol and/or 1, 4-butanediol with adipic acid, glutaric acid, succinic acid, or anhydrides thereof or combinations of these acids.

Polyester-modified polyurethanes may be formed by reacting a polyester diol with at least one diisocyanate, and optionally with one or more extender compounds (also known as chain extenders) having two isocyanate-reactive functional groups. The diisocyanate may be selected from aromatic, aliphatic, and cycloaliphatic diisocyanates and combinations thereof. Useful diisocyanates include, but are not limited to, m-phenylene diisocyanate, 2, 4-toluene diisocyanate, 2, 6-toluene diisocyanate, mixtures of 2, 4-and 2, 6-toluene diisocyanate, 1, 6-hexamethylene diisocyanate, tetramethylene diisocyanate, cyclohexane-1, 4-diisocyanate, any isomer of hexahydrotoluene diisocyanate, isophorone diisocyanate, any isomer of hydrogenated diphenylmethane diisocyanate (methylene-bis-cyclohexyl isocyanate), naphthalene-1, 5-diisocyanate, 1-methoxyphenyl-2, 4-diisocyanate, any isomer of diphenylmethane diisocyanate (including 2, 2' -diphenylmethane diisocyanate, toluene diisocyanate, mixtures thereof, and mixtures thereof, 2, 4 ' -diphenylmethane diisocyanate, and 4, 4 ' -diphenylmethane diisocyanate), diphenylene diisocyanates (including 2, 2 ' -, 2, 4 ' -, and 4, 4 ' -diphenylene diisocyanate), 3 ' -dimethoxy-4, 4 ' -diphenyl diisocyanate, and 3, 3 ' -dimethyl-diphenylmethane-4, 4 ' -diisocyanate, tetramethylxylene diisocyanate (including m-TMXDI and p-TMXDI), xylylene diisocyanate, and combinations thereof. In one embodiment, the diisocyanate comprises diphenylmethane diisocyanate or a mixture of isomers thereof. Polyisocyanates having more than two isocyanate groups, such as 1, 2, 4-benzene triisocyanate, may be included at low levels, but it is preferred to employ only diisocyanates.

Preferably, the reaction mixture of polyester diol and diisocyanate further comprises one or more extender molecules having two groups reactive with isocyanate functional groups selected from active hydrogen-containing groups such as primary amine groups, secondary amine groups, thiol groups and hydroxyl groups. The molecular weight of the chain extender is preferably from about 60 to about 400. Alcohols and amines are preferred. Examples of useful extender compounds include, but are not limited to, diols, dithiols, diamines, or compounds having a mixture of hydroxyl, thiol, and primary or secondary amine groups such as aminoalcohols, aminoalkylthiols, and hydroxyalkylthiols. Specific examples of such materials include, but are not limited to, ethylene glycol, diethylene glycol, higher polyethylene glycol analogs such as triethylene glycol, propylene glycol, dipropylene glycol, and higher polypropylene glycol analogs such as tripropylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 3-butanediol, 1, 6-hexanediol, 1, 7-heptanediol, neopentyl glycol, dihydroxyalkylated aromatic compounds such as 4, 4 '-isopropylidenediphenol (bisphenol A), resorcinol, catechol, hydroquinone, benzenedimethanol, bis (2-hydroxyethyl) ether of hydroquinone and resorcinol, p-xylene- α, α' -diol, bis (2-hydroxyethyl) ether of p-xylene- α, α '-diol, m-xylene- α, α' -diol, and bis (2-hydroxyethyl) and alkylene oxide adducts of said diols, diethyltoluenediamine, polyalkylpolyamines such as ethylenediamine, diethylenetriamine, and triethylenetetramine, difunctional polyoxyalkyleneamines (available from BASF or from Huntsman under the trade name JEFFAMINE *), methylenedianiline p-phenylenediamine, m-phenylenediamine, benzidine, 4' -methylenebis (2-chloroaniline), alkanolamines, and alkylalkanolamines such as ethanolamine, propanolamine, butanolamine, methylethanolamine, ethylethanolamine, methylpropanolamine, t-butylaminoethanol, and combinations thereof. Preferred extenders include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 6-hexanediol, and combinations of these. In addition to difunctional extenders, small amounts of trifunctional extenders such as trimethylolpropane, 1, 2, 6-hexanetriol and glycerol, and/or monofunctional active hydrogen compounds such as butanol or dimethylamine may also be present. The amount of trifunctional extenders and/or monofunctional compounds used is preferably 5.0 equivalent% or less, based on the total weight of the reaction product and active hydrogen-containing groups used.

The polyurethane preferably includes at least about 25% by weight of a polyester diol. In a preferred embodiment, the polyurethane includes at least about 35% by weight polyester segments, and even more preferably, the polyurethane includes at least about 40% by weight polyester segments. The polyester-modified polyurethane may comprise up to about 80 weight percent polyester segments, preferably up to about 65 weight percent polyester segments, and even more preferably up to about 60 weight percent polyester segments. The polyester-modified polyurethane may comprise from about 25 to about 80 weight percent polyester segments, preferably from about 35 to about 65 weight percent polyester segments, and even more preferably from about 35 to about 55 weight percent polyester segments.

In general, the ratio of polyester diol equivalents to extender compound equivalents may vary. Preferably, the ratio of polyester diol equivalents to extender equivalents is from about 1: 1 to about 1: 12, more preferably from about 1: 1 to about 1: 8. To prepare the elastomeric polyurethane, the ratio of polyisocyanate (preferably all diisocyanates) equivalents to the total equivalents of polyester diol and extender is from about 0.96 to about 1.05 equivalents of isocyanate per 1 equivalent of polyester diol and extender combined. More preferably from about 0.98 to about 1.04 equivalents of isocyanate per equivalent of polyester diol and extender combination, and even more preferably from about 1.001 to about 1.01 equivalents of isocyanate per equivalent of polyester diol and extender combination.

The thermoplastic elastomer preferably has a weight average molecular weight of at least about 60,000, more preferably at least about 100,000. The weight average molecular weight of the thermoplastic elastomer is also preferably up to about 500,000, more preferably up to about 300,000.

The thermoplastic elastomer layer may include minor amounts of modifiers and additives. Examples of modifiers and additives include, but are not limited to, plasticizers, fillers, pigments, dyes, light stabilizers, hydrolytic stabilizers, heat stabilizers, antioxidants, rheology modifiers, organic antiblock compounds, fungicides, antimicrobial agents (including bactericides and the like), mold release agents, waxes such as montan ester or diamide waxes, processing aids, and combinations of these. By not using any colorants, a transparent, substantially colorless film can be formed. Colored transparent films can also be formed with transparent colorants. Up to about 40 weight percent of an inorganic filler such as mica or talc may be included.

Examples of hydrolysis stabilizers include two commercially available carbodiimide-based hydrolysis stabilizers known as STABAXOL P and STABAXOL P-100, available from RheinChemie of Trenton, N.J.. Other carbodiimide-or polycarbodiimide-based hydrolysis stabilizers or epoxidized soybean oil-based hydrolysis stabilizers may also be used. The total amount of hydrolysis stabiliser is generally less than 5.0% by weight based on the total weight of the composition.

Plasticizers may be included to increase the flexibility and durability of the final product and to facilitate processing of the material from the resin form into a film or sheet. By way of non-limiting example, those based on butyl benzyl phthalate (which is commercially available, such as Santicizer160 from Monsanto) for example, have proven particularly useful. Whether a plasticizer or a mixture of plasticizers is employed, the total amount of plasticizer is generally less than 20.0% by weight of the total composition, typically less than about 5% by weight of the total composition.

Preferred laminate membranes also include a polymeric barrier layer adjacent to the thermoplastic elastomer layer. The barrier layer comprises at least one polymeric barrier material. The barrier material typically forms crystalline regions or spherulites that make the escape of gas molecules through the layer more difficult. Examples of suitable polymeric barrier materials include, but are not limited to, ethylene vinyl alcohol copolymers, 1, 1-dichloroethylene polymers, acrylonitrile polymers, copolymers of acrylonitrile and methyl acrylate, semi-crystalline polyesters such as polyethylene terephthalate, polyamides, particularly semi-crystalline nylons, crystalline polymers, epoxy-based resorcinol and amines such as N, N-dimethylethylenediamine (DMDEA, JEFFAMINE * 600, 3-amino-N-propanol, and 4-amino-N-butanol), polyurethane engineering thermoplastics such as those available from the Dow Chemical Company under the trademark ISOPLAST *, and combinations of these materials.

Among the preferred polymeric barrier materials are copolymers of ethylene and vinyl alcohol. Preferred copolymers of ethylene and vinyl alcohol have an average ethylene content of from about 25 mole percent to about 48 mole percent. The polymeric release material is preferably an ethylene vinyl alcohol copolymer having a weight average molecular weight of at least about 20,000 and also preferably a weight average molecular weight of up to about 50,000. Commercial products are Nippon GohseiCo., Ltd, SORANOL and EVAL * by Lisle, IL, a subsidiary of Kuraray Co., Ltd (Osaka, Japan).

The barrier layer adjacent to the thermoplastic elastomer layer may include minor amounts of modifiers and additives, including those mentioned above as being suitable for the elastomer layer. Preferably, the polymeric component in the barrier layer is predominantly or substantially exclusively a polymeric barrier material.

The time required for diffusion through the boundary between adjacent laminate layers is affected by the molecular weight of the polymeric component. Therefore, the molecular weight of the polymeric component and the time of thermal annealing are interdependent, and the higher the molecular weight, the longer the time required.

The method may further include the step of forming the laminate membrane from the molten material. At least one thermoplastic elastomer layer and at least one adjacent barrier layer are used to form the preferred laminate in the process of the present invention. In a preferred embodiment, the laminate membrane is formed with an inner layer of a barrier material composition adjacent on each side to the thermoplastic elastomer layer. In other desirable layers, the barrier and thermoplastic elastomer layers may alternate with each other, such as in the preparation of a five-layer laminate membrane in elastomer-barrier-elastomer layers. Layers of other materials may also be included, particularly as the outermost layer. In one embodiment, the five-layer structure provides an innermost layer comprising an ethylene-vinyl alcohol copolymer, a middle layer comprising a thermoplastic polyurethane elastomer on each side of the innermost layer, and an outer layer comprising a blend of ethylene-vinyl alcohol copolymer and thermoplastic polyurethane elastomer on each side of the laminate membrane.

While the laminate membrane prepared by the method of the present invention may be thin or thick, the laminate membrane should be thick enough to provide sufficient wall strength and thin enough to provide sufficient flexibility. Laminate membranes having a thickness of about 20 mils to about 70 mils are generally suitable for blow molding operations. Desirably, each layer is at least about 0.4 mil thick, preferably at least about 0.5 mil thick, more preferably at least about 0.6 mil thick, and still more preferably at least about 1 mil thick, for both the barrier layer and the adjacent thermoplastic elastomer layer; each of these layers is up to about 3 mils thick, preferably up to 2.5 mils thick, more preferably up to about 2 mils thick, and still more preferably up to about 1.6 mils thick. When the laminate membrane has more than one barrier layer and/or more than one thermoplastic elastomer layer, each of these layers may have these thicknesses.

The laminate membrane annealed in the method of the invention may be flat or may be formed into other shapes. Flat film laminates may be prepared by coextruding two or more layers of the laminate.

The method may also further comprise the step of forming the laminate into a shape with heat prior to the annealing step. In one embodiment, the laminate is formed into a shape by blow molding prior to the annealing step. Generally, the bladder can be formed by first coextruding a layer of flat or tubular laminate film and then blow molding the film or tube into the desired final shape. For example, the liquefied elastomeric material and the liquefied polymeric release material may be coextruded as a parison. A mold having the overall shape and configuration of the desired bladder receives the parison in one position and closes around the parison. The parison is cut at the edge of the die. The die is moved back to a position away from the extrusion die. The open portion of the parison above the mold is then equipped with a blow tube that provides pressurized air or other gas, such as nitrogen. The pressurized air forces the parison against the inner surface of the mold. The material is hardened in the mold to form a bladder having a preferred shape and configuration. The blown and formed laminate is cooled and hardened in the mold, which may be at about 40 ° F to 50 ° F, prior to removal from the mold. At the same time, a new mold is moved into this position to receive the next profile from the parison that has been cut from the first mold.

In addition to blow molding with continuous extrusion, the forming step can employ intermittent extrusion through a reciprocating screw system, a ram accumulator type system, and a accumulator head system; co-injection stretch blow molding; extruded and coextruded sheets, blown film tubes, or profiles. Other forming methods include injection molding, vacuum molding, transfer molding, pressure forming, heat sealing, casting, melt casting, RF welding, and the like.

The flat laminate or shaped laminate is then annealed as described above. In a preferred embodiment, the laminate is annealed at a temperature of up to about 100 ℃, more preferably up to about 140 or 150 ℃.

The laminate may be annealed immediately after extrusion and/or forming, for example, if blow molding is after removal from the mold, or there may be a period of time between when the laminate is formed but before the barrier layer or thermoplastic elastomer layer forms a significant modulus. While the lag time can vary depending on the particular material used, the thickness of the layers in the laminate membrane, and the total laminate thickness, the lag time is generally up to about 60 minutes, more preferably up to about 30 minutes, even more preferably up to about 20 minutes, and still more preferably up to about 15 minutes. The lag time should generally not exceed about 2 hours. When the lag time is longer than about 2 hours, the modulus formation may prevent the laminate membrane from improving the interfacial adhesion during the annealing step. Preferably, the lag time is no more than about 1.5 hours, more preferably no more than about 1 hour.

The invention also provides a laminate in which the composition of one layer has partially diffused into an adjacent layer. In a preferred embodiment, the laminates of the present invention have an interfacial bond strength of at least about 20 lbs/lineal inch.

After the annealing step, the laminate may be subjected to further shaping steps. For example, the annealed flat film may be cut into a desired shape. The two portions of the flat membrane may be sealed at the edges to form the bladder.

The invention further provides an air-bag, in particular an inflatable air-bag, comprising the laminate according to the invention, and an article comprising the air-bag. The bladder may be inflated with gas and permanently sealed. The laminate membrane of the present invention having an annealed layer of a thermoplastic elastomer layer adjacent to a layer of polymeric gas barrier material provides flexibility and resistance to unwanted permeation of gases such as inflation gases. Durable elastomeric films for inflatable bladders are useful in many applications, particularly for inflation or slow inflation applications. By the term "durable" is meant that the film has excellent fatigue failure resistance, i.e., the film can undergo repeated flexing and/or deformation and recover without delaminating along the layer interface of the composite separator film, preferably over a wide temperature range.

The film, whether in sheet form, in the form of a substantially closed container, in the form of a buffer device, in the form of a reservoir, or in other configurations, preferably has a tensile strength of at least about 2500psi, a 100% tensile modulus between about 305 and 3000psi, and/or an elongation of at least about 250% to about 700%.

In particular, the present invention provides an inflatable bladder for inflating and cushioning, for example for inflating objects such as sports balls and cushioning footwear or a hydraulic reservoir. The bladder has a membrane comprising at least one layer of elastomeric material, preferably a polyester modified polyurethane material, and an adjacent layer of polymeric barrier material. The film of the present invention has elastic mechanical properties that allow it to absorb high forces repeatedly and reliably during use without degradation or fatigue failure. Excellent stability of the film during cyclic loading is particularly important for these applications. The barrier film has a low gas permeability allowing it to remain inflated and thus provide cushioning or inflation for substantially the expected life of the article without the need for periodic re-inflation or re-pressurization of the air bag and thus may be permanently sealed.

Inflatable bladders can provide inflation and cushioning in a wide variety of applications, including (but not limited to) bladders used in: inflatable objects such as balls (including soccer balls, basketballs and football balls), internal tubes, soft drift equipment such as tubes or rubber boats, elements as medical equipment such as catheterized balloons, as part of furniture such as tables and chairs, as part of bicycles or saddles, as part of protective equipment including shin guards and helmets, as support elements for articles of furniture and in particular for lumbar support, as part of most complementary or orthopaedic equipment, as part of vehicle tyres, in particular the outer layers of tyres, and as part of certain recreational equipment such as wheels for coaxial or four-wheeled skates. The reservoir, in particular the hydraulic reservoir, may be used in a car parking system, a car brake system, an industrial hydraulic reservoir or in other applications where there is a difference in pressure between two potentially different fluid media. The laminate membrane divides the hydraulic reservoir into two chambers or compartments, one of which contains a gas such as nitrogen and the other of which contains a liquid. Another important application for inflatable bladders is footwear.

Footwear, in particular shoes, generally include two primary elements: a vamp and a sole. The general purpose of the upper is to snugly and comfortably enclose the foot. Ideally, the upper should be made of an attractive, highly durable, comfortable material or a combination of these materials. Soles constructed from durable materials are designed to provide traction and protect the foot during use. The sole also generally plays an important role in providing enhanced cushioning and shock absorption during athletic activities to protect the wearer's foot, and leg from significant forces generated. Impact forces generated during running can be as high as 2 or 3 times the weight of the wearer, while other athletic activities such as playing basketball can generate forces 6 to 10 times the weight of the wearer. To provide these functions, the sole typically includes a midsole or insole having a cushioning effect and an outsole having a drag surface.

The cushion bladder of the present invention may be used in a midsole or insole of a shoe. One sole structure with a suitable impact response is a sole or sole insert that includes a bladder element containing a fluid or preferably a gaseous fluid. The bladder element is either encapsulated during the formation of the foam midsole or glued in a shallow cavity in the foam midsole, which typically has another piece of foam glued on top. Such resilient, shock-absorbing materials or elements may also be applied to an insole portion of the footwear, which is generally defined as the portion of the upper that directly lines the plantar surface of the foot.

In cushioning elements for footwear and other uses, the membrane is preferably capable of containing a captive gas for a considerable period of time. In a highly preferred embodiment, for example, the membrane should not lose more than about 20% of the initial inflation gas pressure over a period of about 2 years. In other words, a product that is initially inflated to a stable pressure of 20.0-22.0psi should maintain a pressure of 16.0-18.0psi for at least about 2 years.

The bladder or cushioning device may be inflated with air, or a component of air such as nitrogen, or with a super gas. When used as a cushioning device for footwear, such as shoes, the bladder may preferably be inflated with nitrogen to an internal pressure of at least about 3psi, preferably at least about 5psi, and up to about 50 psi. Preferably, the bladder is inflated to an internal pressure of about 5psi to about 35psi, more preferably about 5psi to about 30psi, still more preferably about 10psi to about 30psi, and still more preferably about 10psi to about 25 psi. It will be appreciated by the skilled artisan that in applications other than footwear applications, the desired and preferred pressure ranges may vary widely and may be determined by those skilled in the particular application. For example, the accumulator pressure may be up to about 1000 psi. The reservoir pressure is preferably up to about 500 psi. For accumulator applications, the preferred pressure range is about 200psi to about 1000psi, but pressures as low as about 25psi are also possible depending on the design of the accumulator. After inflation, the inflation port of the inflatable bladder, which requires permanent sealing, can be sealed, for example, by RF welding.

In order for the airbag to remain permanently inflated, the gas permeability must be suitably low. In a preferred embodiment, the gas permeability of the airbag membrane should be less than about 15 cubic centimeters per square meter atmosphere per day (cc/m) for an inflation gas, preferably air or nitrogen²Atm · day), preferably less than about 6cc/m²Atm-day, especially less than about 4cc/m²Atm-day, more preferably less than about 2.5cc/m²Atm. day, still more preferably less than about 1.5cc/m²Atm.day, particularly preferably less than about 1cc/m²Atm · day. One acceptable method of measuring the relative permeability, and diffusion of different film materials is described in ASTM D-1434. While nitrogen is the preferred captive gas for many embodiments and as a benchmark for gas transmission according to ASTM D-1434, membranes may contain many different gases and/or liquids.

The invention is further described in the following examples. These examples are merely illustrative and in no way limit the scope of the invention described in the claims. All parts are parts by weight unless otherwise indicated.

Examples

The air bag was blow molded with a layer of EVAL * F101 ethylene vinyl alcohol copolymer (EVOH) (available from Evalca company, Lisle, Ill.) and a layer of a blend of 3 wt.% F101 adjacent to the EVOH layer on each side (processed at 215 ℃) in PELLETHANE * 2355-80AE polyurethane (available from Dow Chemical, Midland, Mich.). In example 1, the bladder was removed from the mold and, after a 6 minute lag time, placed in a convection oven at 140 ℃ for 20 minutes. Comparative example a was not annealed.

To test the interfacial bond between the layers, a 1 inch wide strip was cut from each bladder. The strip is cut transversely across the release layer with a blade. The spacer layer has two interfacial surfaces: an inner interface cooled by air to the inside of the parison and an outer interface cooled by the mold from the outside of the parison. To test the interfacial adhesion, one polyurethane layer was pulled away from the barrier layer so that the jaws of the tensile tester grasped the other side of the polyurethane layer and test strip containing the barrier layer and the other polyurethane layer, respectively. Once the sample was placed in the tensile fixture, the crosshead was moved at a rate of 2 "/min. The sensor placed on the holding fixture records the force required to continuously pull the separated polyurethane layer evenly from the isolation interface along a narrow 1 "wide strip. When the peel force leveled off, the test was terminated and the force per linear inch was recorded.

The peel force was recorded for the inside and outside interfaces of the balloon.

Examples	Inside peel adhesion (pounds per linear inch)	Outside peel adhesion (pounds per linear inch)
			A	4.0	5.2
1	17.6	17.6

Example 2

A sealed, inflated balloon was formed from the annealed, blow-molded balloon prepared in example 1 by trimming an excess flash weld (flash) around the part. The parts that were punched with the trimmed edges were inserted into an inflation machine. A needle adapted to the molded blow hole is automatically inserted. Nitrogen gas is inflated into the bladder until a predetermined pressure is reached. A multi-chambered balloon with different pressures is then provided by closing the RF around the inflation tube and applying RF energy long enough to melt the polymer and seal the passage. More gas is then inflated into the airbag until the next highest pressure is achieved. At this point, another set of RF dies is lowered onto another gas-filled tube to RF seal the channel. This process is repeated until all of the pressure chambers in the bladder have been filled and sealed.

Example 3

A shoe was prepared from the sealed, inflated bladder of example 2 by first cleaning and drying the inflated bladder. The base coat is then sprayed onto the balloon and dried. The top and bottom were painted to provide color and then air dried. To assemble the shoe, the bladder and outsole are inserted into a mold, the TPU foam is molded and cured around the bladder and on the outsole. The pre-stitched upper is glued under pressure to the midsole/outsole and cooled in the air channels.

The invention has been described in detail with reference to the preferred embodiments. However, it should be understood that: variations and modifications can be made within the spirit and scope of the invention.

Claims (29)

1. A method of improving the bond between two adjacent layers of a laminate membrane, comprising the steps of:

(a) forming a laminate having a first thermoplastic layer adjacent to a second thermoplastic layer;

(b) annealing the laminate at a temperature above the thermal transition temperature of at least one polymeric component of at least one layer for a time sufficient to allow partial diffusion of at least one polymeric component into an adjacent layer.

2. The method of claim 1, wherein the annealing temperature is at least 50 ℃ above the thermal transition temperature of the at least one polymeric component.

3. The method of claim 1, wherein at least one of the first and second layers comprises a semi-crystalline polymeric component.

4. The method of claim 1, wherein the first layer is a thermoplastic elastomer layer and the second layer is a thermoplastic polymeric barrier layer.

5. The method of claim 1, wherein the laminate is annealed for at least 15 minutes.

6. The method of claim 1, wherein the laminate is annealed for at least 30 minutes.

7. The method of claim 1, wherein the laminate is annealed for at least 40 minutes.

8. The method of claim 1, wherein said laminate membrane is annealed at a temperature above the thermal transition temperature of at least one component of each of said first and second layers.

9. The method of claim 1, wherein said laminate is annealed at a temperature at least 80 ℃ above the thermal transition temperature of said at least one polymeric component of said at least one layer.

10. The method of claim 4, wherein said laminate is formed into a shape by blow molding prior to said annealing step.

11. The method of claim 10, wherein the annealing step is performed within 2 hours of blow molding.

12. The method of claim 10, wherein the annealing step is performed within 1.5 hours of blow molding.

13. The method of claim 10, wherein the annealing step is performed within 1 hour of blow molding.

14. The method of claim 10, wherein the annealing step is performed within 30 minutes of blow molding.

15. The method of claim 10, wherein the annealing step is performed within 15 minutes of blow molding.

16. The method of claim 4, wherein the annealing step is performed at a temperature of at least 100 ℃.

17. The method of claim 4, wherein the annealing step is performed at a temperature of up to 150 ℃.

18. The method of claim 1, wherein at least one polymeric component of at least one of the first and second layers has a glass transition temperature of-30 ℃ to 20 ℃.

19. The method of claim 4, wherein the thermoplastic elastomer layer comprises a material selected from the group consisting of: polyurethanes made with polyesters, polyethers, and polycarbonate diols, flexible polyolefins, styrenic thermoplastic elastomers, polyamide-ether elastomers, polymeric ester-ether elastomers, flexible ionomers, thermoplastic vulcanizates, EPDM vulcanized in polypropylene, flexible polyvinyl chloride homopolymers and copolymers, flexible acrylic polymers, and combinations thereof.

20. The method of claim 4, wherein the thermoplastic polymeric barrier layer comprises a material selected from the group consisting of: ethylene vinyl alcohol copolymers, 1, 1-dichloroethylene polymers, acrylonitrile polymers, copolymers of acrylonitrile and methyl acrylate, semi-crystalline polyesters, polyethylene terephthalate, polyamides, crystalline polymers, epoxy resins based on N, N-dimethylethylenediamine and resorcinol, polyurethane engineering thermoplastics, and combinations thereof.

21. The laminate formed according to the method of claim 4, wherein the first layer comprises a thermoplastic polyurethane prepared from a polyester diol and the second layer comprises an ethylene vinyl alcohol copolymer.

22. The laminate of claim 21, further comprising at least one third layer comprising a thermoplastic polyurethane prepared from a polyester diol adjacent to the second layer.

23. The laminate formed by the method of claim 10, wherein the first layer comprises a thermoplastic polyurethane made from a polyester diol and the second layer comprises an ethylene vinyl alcohol copolymer, and further wherein the blow molding step provides an air bladder that is sealed and inflated after the annealing step.

24. The laminate of claim 23 wherein said polyurethane comprises at least 50% by weight of a polyester diol.

25. The laminate of claim 23 wherein said polyurethane comprises at least 60% by weight of a polyester diol.

26. The laminate of claim 23 wherein said polyester diol has a weight average molecular weight of at least 2000.

27. The laminate of claim 23, wherein said laminate has a gas transmission rate of less than 6 cubic centimeters per square meter atm day.

28. A ball comprising an air bladder made from the laminate of claim 23.

29. A shoe comprising an air bladder prepared from the laminate of claim 23.