WO2007079270A2 - Thermoplastic polyurethane powder compostions and uses - Google Patents

Abstract

Thermoplastic powder compositions and related processes of the invention comprise at least one thermoplastic polyurethane having a melt flow index of at least about 8 g/10 min when tested according to ASTM D1238 at 190 °C and a weight of 2.16 kg; at least one internal lubricant in an amount of up to about 5 weight % based on total weight of the composition; and, optionally, at least one flow agent or other components. Such thermoplastic powder compositions are suitable for formation into a variety of articles using, for example, high velocity impact fusion or slush molding techniques.

Description

THERMOPLASTIC POL YURETHANE POWDER COMPOSITIONS AND USES

CLAIM OF PRIORITY

[0001] This application claims priority from U.S. Provisional Patent

Application Serial Number 60/727,367 bearing Attorney Docket Number 12004007 and filed on October 17, 2005, which is incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to thermoplastic polyurethane powder compositions and uses thereof.

[0003] Over the past several decades, the use of polymers has transformed the world. Polymer science has rapidly evolved to make thousands of different thermoplastic and thermosetting products within the four corners of polymer physics: thermoplastic plastics, thermoplastic elastomers, thermoset plastics, and thermoset elastomers.

[0004] No large scale production of any polymer or articles therefrom can rest on current ingredients or processing conditions. Reduction of cost, improvement of productivity, delivery of better performing, lower cost products all drive the polymer science industry. With the advent of new materials and associated processes, it is often beneficial to replace older polymeric materials with materials having improved properties, processing capabilities, and/or processing efficiencies in particular applications and associated processes.

[0005] For instance, in certain applications, replacements for polyvinyl chloride (PVC) are desired. Articles formed from PVC, while relatively inexpensive and easy to process, tend to become brittle (and hence exhibit a brittle failure mode) when used at lower temperatures. Thus, the use of PVC for forming articles subject to cold climates and other relatively low temperatures can be problematic for certain applications requiring ductile failure modes.

[0006] In particular, one application where ductile failure modes are preferred involves manufacture of articles for passenger compartments of vehicles such as automobiles, airplanes, trucks, farm equipment, construction equipment, et cetera.

Polymeric materials are used to manufacture many parts and subassemblies within such passenger compartments. For example, instrument panels, door panels, armrests, headrests, center consoles, and air bags, et cetera can be made from one or more polymeric materials.

[0007] A subcomponent of such articles often takes the form of a "polymeric skin." Polymeric skins can provide the outer surface of larger articles, being filled with molded foam or other cushiony materials to provide body and a sculpted appearance to the overall article. For instance, padded or cushioned articles within passenger compartments, such as instrument panels, door panels, and the like, have been made by providing a powdered PVC slush-molded skin. The skin is held in place over a substrate and then back-filled with a foam (e.g., urethane foam) material in an injection process in which the edges of the skin are sealed in order to provide a finished product. The finished product includes the skin with the padded foam backing bonded to the substrate, which may include the edges of a door panel, the edges of an instrument panel, or the like. Reference to the use of polymeric skins in this manner can be found in, e.g., U.S. Patent Publication No. US 2002/0125734 Al. [0008] When materials exhibiting brittle failure modes at some or all temperatures of intended use are used in making polymeric skins for such applications, however, they pose a risk for the passenger in the event of impact, or other event leading to an article's failure. This risk is heightened by using brittle materials due to the tendency of brittle materials to shatter upon failure and fragment into many tiny pieces, oftentimes having jagged or sharp edges. Generation of such shrapnel jeopardizes safety of those within and out of the passenger compartment. [0009] As such, a prerequisite to selecting materials for use in passenger vehicle manufacturing often involves testing to determine a material's suitability for use in a variety of environments. Materials for one article in particular within passenger compartments - air bags - are carefully screened under a wide variety of environmental conditions. A material's performance at temperatures of about -40°C (-40⁰F) and less is an important threshold considered in determining a material's ability to pass these tests. PVC often fails such tests due to its brittle tendency at lower use temperatures. Yet, PVC is advantageous as compared to conventional substitutes due to its relatively low cost. Thus, alternative materials are desired. [00010] Not only are further materials desired, but efficient and replicable methods for production of articles therefrom are also desired. A wide variety of processes are known for the manufacture of polymeric components such as those described above. One particular process for formation of polymeric skins is termed high velocity impact fusion (HVIF). In this process, a polymer powder is fluidized and melted in an inert gas such as nitrogen before being accelerated into a mold or other tool in which the powder accumulates on one or more target surfaces and then solidifies into a continuous film. Typically the target surface is maintained at approximately room temperature in order to promote film solidification. See, e.g., U.S. Patent No. 5,285,967.

[00011] HVIF has been used to impart polymeric coatings onto articles in order to protect underlying surfaces or materials coming into contact with the underlying surface from damage (e.g., contamination). Often, the polymeric coating provides a relatively clean, non-toxic surface and is made from a relatively inert material. For example, polyethylene is coated on the inside of steel railroad cars using HVIF in order to prevent foodstuff transported by the railroad car from becoming contaminated.

[00012] It is desirable to expand the application of HVIF to further materials due to the processing advantages associated with the method and its ability to form articles having desired surface characteristics. This is particularly true for those applications requiring surface finishes of a particular caliber (e.g., one that is smooth and uniform or one that has a uniform leathery appearance). To date, however, expansion of HVIF to include preparation of articles for industries such as those involving manufacture of polymeric articles used in passenger compartments has been difficult because suitable powder compositions for this unique process were not yet known. As such, injection molding has become a prevalent method for formation of polymeric skins and other polymeric articles in these applications due to the limitations and disadvantages associated with HVIF and other manufacturing techniques (e.g., vacuum forming, slush molding, rotational molding, and spraying). Again, reference is made to U.S. Patent Publication No. US 2002/0125734 Al.

BRIEF SUMMARY OF THE INVENTION

[00013] Advantageously, the invention provides a thermoplastic powder composition suitable for formation into an article using high velocity impact fusion. Such powder compositions have a uni-modal particle size distribution and comprise at least one thermoplastic polyurethane having a melt flow index of at least about 8 g/10 min when tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg; at least one internal lubricant in an amount of up to about 5 weight % based on total weight of the composition; and, optionally, at least one flow agent or other components (e.g., heat stabilizers, light stabilizers, pigments, antioxidants, plasticizers, fillers, and mattening agents).

[00014] Other thermoplastic powder compositions are also facilitated by the present invention. Depending on the application, the powder composition can have a uni-modal particle size distribution or a bi-modal particle size distribution. [00015] For example, the invention provides a thermoplastic powder composition suitable for formation into an article using slush molding. Such powder compositions have a bi-modal particle size distribution and comprise at least one thermoplastic polyurethane having a melt flow index of at least about 8 g/10 min when tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg; at least one internal lubricant in an amount of up to about 5 weight % based on total weight of the composition; and, optionally, at least one flow agent or other components (e.g., heat stabilizers, light stabilizers, pigments, antioxidants, plasticizers, fillers, and mattening agents).

[00016] In exemplary embodiments of the invention, the thermoplastic polyurethane comprises aliphatic thermoplastic polyurethane or aromatic thermoplastic polyurethane. In further embodiments, the thermoplastic polyurethane comprises polyether-based thermoplastic polyurethane (e.g., an aromatic polyether- based thermoplastic polyurethane) or polyester-based thermoplastic polyurethane (e.g., an aliphatic polyester-based thermoplastic polyurethane).

[00017] While the amounts of the individual components will vary according to the desired application and process, in one embodiment the thermoplastic powder composition comprises about 0.01 to about 1.0 weight % of an internal lubricant such as, for example, mono- and di-stearyl acid phosphate. Preferably, although not necessarily, the composition is essentially free of components prone to blooming migration in articles prepared therefrom.

[00018] In further embodiments, the powder composition can be a powder composition blend. Powder composition blends of the invention comprise at least one thermoplastic polyurethane and at least one other polymer (e.g., polyvinyl chloride). In an exemplary embodiment, the other polymer comprises greater than about 10 weight % of the total composition. For example, the other polymer can be polyvinyl chloride in an amount up to about 90 weight % of the total composition. In exemplary embodiments of powder composition blends, the composition comprises about 5 to about 50 weight %, about 10 to about 30 weight %, or still further about 15 to about 25 weight % of the thermoplastic polyurethane based on total weight of the composition. Other components can also be present, including for example melt- processible rubber.

[00019] A variety of articles can be prepared from thermoplastic powder compositions of the invention. For example, polymeric skin subcomponents of further articles for passenger compartments of a vehicle can be formed from the thermoplastic powder compositions. Such further articles include instrument panels, door panels, armrests, headrests, center consoles, and air bags for a passenger compartment of a vehicle. Compositions of the invention advantageously provide alternatives to and advantages as compared to conventional materials used for such purposes.

[00020] Processes of the invention include those for preparing the thermoplastic powder compositions. Such processes include steps of providing a thermoplastic polyurethane, mixing the thermoplastic polyurethane with one or more optional components, and transforming the thermoplastic polyurethane and optional components into a powder having a uni-modal or otherwise predetermined particle size distribution. In an exemplary embodiment, the composition is transformed into a powder using cryogenic grinding, screening, and recycling steps. [00021] Processes for preparing articles from the thermoplastic powder composition include those using a high velocity impact fusion, fluidized bed powder coating, electrostatic spray, thermal spray, slush molding, or rotational molding technique. According to exemplary embodiments of the invention, an external mold release agent is not necessary or utilized to form such articles.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [00022] FIGURE 1 is a uni-modal particle size distribution associated with powder compositions useful for formation of articles according to a high velocity impact fusion technique according to the invention.

[00023] FIGURE 2 is a bi-modal particle size distribution associated with powder compositions useful for formation of articles according to a slush molding technique according to the invention. [00024] FIGURE 3 is a schematic flow diagram of an exemplary process for formation of powder compositions of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[00025] Compositions

[00026] Thermoplastic polyurethane (TPU) powder compositions of the invention comprise at least one base TPU and one or more optional components, selected according to the intended use of the composition.

[00027] Base TPU

[00028] TPU is a desirable thermoplastic elastomer as it exhibits high tensile and tear strength, high flexibility at low temperatures, and extremely good abrasion and scratch resistance. TPU is also relatively stable against oil, fats and many solvents, as well as ultraviolet radiation. Because of these desirable features, TPU can be beneficially used for a number of end use applications, such as those in automotive and the footwear industries.

[00029] For simplicity, the term "polyurethane" as used herein includes polymers containing urethane (also known as carbamate) linkages, urea linkages, or combinations thereof (i.e., in the case of poly(urethane-urea)s). Thus, thermoplastic polyurethanes of the invention contain at least urethane linkages and, optionally, urea linkages.

[00030] A wide variety of TPU chemistries are suitable for use as the base TPU in the invention. For example, a number of aliphatic and aromatic chemistries can be used. One or more TPU chemistries can be used to form the base TPU for compositions of the invention.

[00031] The term "aromatic" refers to TPUs derived from mononuclear aromatic hydrocarbon groups or polynuclear aromatic hydrocarbon groups. The term includes those TPUs derived from arylene groups. The term "arylene group" means a divalent aromatic group.

[00032] The term "aliphatic" refers to TPUs derived from saturated or unsaturated, linear, branched, or cyclic hydrocarbon groups. This term is used to encompass those TPUs derived from alkylene (e.g., oxyalkylene), aralkylene, and cycloalkylene (e.g., oxycyclo alkylene) groups, for example. The term "alkylene group" means a saturated, linear or branched, divalent hydrocarbon group.

Particularly preferred alkylene groups are oxyalkylene groups. The term "oxyalkylene group" means a saturated, linear or branched, divalent hydrocarbon group with a terminal oxygen atom. The term "aralkylene group" means a saturated, linear or branched, divalent hydrocarbon group containing at least one aromatic group. The term "cycloalkylene group" means a saturated, linear or branched, divalent hydrocarbon group containing at least one cyclic group. The term "oxycycloalkylene group" means a saturated, linear or branched, divalent hydrocarbon group containing at least one cyclic group and a terminal oxygen atom.

[00033] According to one embodiment of the invention, a TPU is obtained by reacting a difunctional isocyanate composition with at least one difunctional polyhydroxy compound and optionally a chain extender in such amounts that the isocyanate index is between about 90 and about 110, preferably between about 95 and about 105, and most preferably between about 98 and about 102. [00034] The term "difunctional" as used herein means that the average functionality of the isocyanate composition and the polyhydroxy compound is about 2

[00035] The term "isocyanate index" as used herein is the ratio of isocyanate groups over isocyanate-reactive hydrogen atoms present in a composition, given as a percentage. In other words, the isocyanate index expresses the percentage of isocyanate actually used in a composition with respect to the amount of isocyanate theoretically required for reacting with the amount of isocyanate-reactive hydrogen used in a composition. It should be observed that the isocyanate index as used herein is considered from the point of view of the actual polymer forming process involving the isocyanate ingredient and the isocyanate-reactive ingredients. Any isocyanate groups consumed in a preliminary step to produce modified polyisocyanates (including such isocyanate-derivatives referred to in the art as quasi- or semi- prepolymers) or any active hydrogens reacted with isocyanate to produce modified polyols or polyamines, are not taken into account in the calculation of the isocyanate index. Only the free isocyanate groups and the free isocyanate-reactive hydrogens present at the actual elastomer forming stage are taken into account. [00036] In this embodiment, the difunctional polyhydroxy compound has a weight average molecular weight of between about 500 and about 20,000, and is selected from diols such as polyesteramides, polythioethers, polycarbonates, polyacetals, polyolefins, polysiloxanes, polybutadienes and, preferably, polyesters and polyethers, or mixtures thereof. Other dihydroxy compounds such as hydroxyl-ended styrene block copolymers like known SBS, SIS, SEBS, or SIBS block copolymers may be used as well.

[00037] Mixtures of two or more compounds of such or other functionalities and in such ratios that the average functionality of the total composition is about 2 may also be used as the difunctional polyhydroxy compound. For polyhydroxy compounds, the actual functionality may be somewhat less than the average functionality of the initiator due to some terminal unsaturation. Therefore, for example, small amounts of trifunctional polyhydroxy compounds may be present as well in order to achieve the desired average functionality of the composition. [00038] Polyether diols that may be used include products obtained by the polymerization of a cyclic oxide, for example ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran in the presence, where necessary, of difunctional initiators. Suitable initiator compounds contain two active hydrogen atoms and include water; butanediol; ethylene glycol; propylene glycol; diethylene glycol; Methylene glycol; dipropylene glycol; 1,3-propane diol; neopentyl glycol; 1,4- butanediol; 1,5-pentanediol; 1,6-pentanediol; and the like. Mixtures of initiators and/or cyclic oxides may be used.

[00039] Especially useful polyether diols include polyoxypropylene diols and poly(oxyethylene-oxypropylene) diols obtained by the simultaneous or sequential addition of ethylene or propylene oxides to difunctional initiators. Random copolymers having oxyethylene contents of about 10-80 weight %, block copolymers having oxyethylene contents of up to about 25 weight % and random/block copolymers having oxyethylene contents of up to about 50 weight %, based on the total weight of oxyalkylene units, may be mentioned, in particular those having at least part of the oxyethylene groups at the end of the polymer chain. Other useful polyether diols include polytetramethylene diols obtained by the polymerization of tetrahydrofuran. Also suitable are polyether diols containing low unsaturation levels (i.e. less than about 0.1 milliequivalents per gram diol).

[00040] Other diols that may be used comprise dispersions or solutions of addition or condensation polymers in diols of the types described above. Such modified diols, often referred to as "polymer diols" include products obtained by the in-situ polymerization of one or more vinyl monomers, for example styrene and acrylonitrile, in polymeric diols, for example polyether diols, or by the in-situ reaction between a polyisocyanate and an amino- and/or hydroxyfunctional compound, such as triethanolamine, in a polymeric diol.

[00041] Polyoxyalkylene diols containing from about 5-50 weight % of dispersed polymer are useful as well. Particle sizes of the dispersed polymer of less than 50 microns are preferred.

[00042] Polyester diols that may be used include hydroxyl-terminated reaction products of dihydric alcohols such as ethylene glycol; propylene glycol; diethylene glycol; 1,4-butanediol; neopentyl glycol; 2-methylpropanediol;

3-methylpentane-l,5-diol; 1,6-hexanediol; cyclohexane dimethanol; and mixtures of such dihydric alcohols and dicarboxylic acids or their ester-forming derivatives (e.g., succinic, glutaric, and adipic acids or their dimethyl esters, sebacic acid, phthalic anhydride, tetrachlorophthalic anhydride, dimethyl terephthalate and mixtures thereof).

[00043] Polyesteramides may be obtained by the inclusion of aminoalcohols such as ethanolamine in polyesterification mixtures.

[00044] Polythioether diols that may be used include products obtained by condensing thiodiglycol either alone or with other glycols, alkylene oxides, dicarboxylic acids, formaldehyde, amino-alcohols, or aminocarboxylic acids.

[00045] Polycarbonate diols that may be used include those prepared by reacting glycols such as diethylene glycol, triethylene glycol, or hexanediol with formaldehyde. Suitable polyacetals may also be prepared by polymerizing cyclic acetals.

[00046] Suitable polyolefin diols include hydroxy-terminated butadiene homo- and co-polymers.

[00047] Suitable polysiloxane diols include polydimethylsiloxane diols.

[00048] Suitable difunctional chain extenders include aliphatic diols, such as ethylene glycol; 1,3-propanediol; 1,4-butanediol; 1,5-pentanediol;

1,6-hexanediol; 1,2-propanediol; 2-methylpropanediol; 1,3-butanediol;

2,3-butanediol; 1,3-pentanediol; 1,2-hexanediol; 3-methylpentane-l,5-diol; diethylene glycol; dipropylene glycol; and tripropylene glycol, and aminoalcohols such as ethanolamine, N-methyldiethanolamine, and the like. Of these, 1,4-butanediol is preferred.

[00049] According to another embodiment, the TPU powder composition comprises an aromatic, polyether-based TPU. According to yet another embodiment, the TPU powder composition comprises an aliphatic, polyester-based TPU. The latter TPU chemistry is particularly desirable due to the ability to more precisely and accurately control melt flow properties (e.g., melt flow index (MFI)) thereof as compared to the former chemistry.

[00050] A number of suitable TPU compositions are commercially available.

Depending on the use for which the powder composition will be applied, often the MFI of the TPU composition is considered when selecting a TPU. Generally, according to exemplified uses described further below, it is desirable for a TPU to have a MFI of at least about 8 g/10 min when tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg. In further embodiments, it is desirable for a TPU to have a MFI of at least about 10 g/10 min when tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg. In still further embodiments, it is desirable for a TPU to have a MFI of at least about 12 g/10 min when tested according to ASTM D 1238 at 19O⁰C and a weight of 2.16 kg.

[00051] BASF Corp. (Wyandotte, MI) and other chemical companies offer a wide variety of suitable TPUs for use in the invention. One exemplary line of TPU grades is available from BASF Corp. under the ELASTOLLAN trade designation. [00052] Although commercial supplies of TPUs having a MFI in the preferred range are available, TPUs having a lower MFI may also be used as the base TPU. In order to sufficiently increase the MFI to a desired level, however, small amounts of water may be injected into an extruder containing the molten TPU. Addition of water in this way causes the molten TPU polymer backbone to undergo chain scission, which reduces molecular weight and increases the MFI of the TPU. Chain scission in this manner can be further accelerated by increasing temperature and screw speed of the extruder so used. However, in order to avoid increasing the MFI of the TPU in this manner to a level that negatively impacts the resulting physical properties of the article formed therefrom, other methods and materials are typically preferred. [00053] Generally, the prepared or supplied base TPU will be provided in a non-powdery form (e.g., as pellets or granules). Thus, the base TPU and other optional components described below are transformed into a powder after mixing and prior to use. The powder formation process is also described further below. [00054] Other Components

[00055] Other components can be included in compositions of the invention to improve or obtain certain properties of the composition or components therein, such as the desired MFI of the base TPU. It is to be understood that, depending on the manufacturing method for the base TPU or commercial source thereof, one or more additional components may already be present in the base TPU. If other desired components are not present, however, they may be added to the base TPU when preparing compositions of the invention.

[00056] These components include, for example, internal and other lubricants, flow agents, heat stabilizers, light stabilizers, pigments (e.g., carbon black), antioxidants, plasticizers, fillers (e.g., talc and CaCO₃), and mattening agents (e.g., polyurea powders and various silicas). Those skilled in the art can, without undue experimentation, select various components and various amounts of other components to fulfill desired properties.

[00057] For example, materials that reduce porosity of a molten film of the composition during formation of articles therefrom are beneficially added when the MFI of the composition does not alone sufficiently minimize entrapment of air between the molten film and surface on which it is being formed. If too much air becomes entrapped, porosity will be apparent on the outer surface of the article formed. In many applications, particularly those involving parts for consumer applications, little porosity can be tolerated before the article is rejected for aesthetic reasons. While plasticizers may be added for this purpose, it is desired to minimize their use in certain applications due to their tendency to migrate from the material's surface (e.g., often referred to as "blooming," a phenomenon that causes fogging of windshields when used in vehicle instrument panels) and negatively impact resultant physical properties of articles prepared therefrom.

[00058] According to a preferred embodiment of the invention, at least one lubricant is incorporated into the composition in order to decrease porosity in resulting articles without the disadvantages associated with effecting lower porosity by way of increasing the TPU' s MFI alone. Another advantage of incorporating a lubricant within the composition is the ability to reduce or eliminate the need for use of an external mold release agent during formation of molded articles therefrom. [00059] In one embodiment, compositions of the invention comprise up to about 5 weight % based on total weight of the composition of at least one internal lubricant. For example, a composition comprising about 0.01 to about 1.0 weight % mono- and di-stearyl acid phosphate (e.g., AX-71, available from Asahi Denka Kogyo K.K., Tokyo, Japan, under the ADK STAB trade designation) based on total weight of the composition was found useful according to the invention. Although AX-71 is not marketed as an internal lubricant, it has been discovered that it is useful for this purpose. When the TPU comprises an aliphatic chemistry, generally less lubricant is needed to obtain the same results as when lubricant is used in conjunction with TPUs comprising aromatic chemistries.

[00060] According to another embodiment of the invention, at least one flow agent is incorporated into the composition in order to decrease porosity in resulting articles without the disadvantages associated with effecting lower porosity by way of increasing the TPU' s MFI alone. For example, a composition comprising precipitated amorphous silica (e.g., PS-200, available from Glassven C. A., a Venezuelan company, under the PIROSIL trade designation) can beneficially be used according to the invention.

[00061] Compositions containing one or more of these optional components are capable of eliminating the blooming phenomenon referenced above with respect to plasticizers. Thus, in preferred embodiments, plasticizers and other components prone to such migration are excluded from or minimized in compositions of the invention. Such other components include certain antioxidants, hindered amine light stabilizers, UV-stabilizers, and other compounds known to promote undesirable blooming.

[00062] Blends

[00063] Compositions of the invention include powder composition blends comprising at least one base TPU and at least one other polymer. Such blends are provided in a powdered form to facilitate their use in a variety of article-forming processes providing substantial benefits as discussed throughout. For example, one preferred use involves formation of an article therefrom using the unique HVIF technique. Optional components described above can also be included within powder composition blends of the invention to obtain desired properties and facilitate efficient processing of the compositions as desired. The ultimate blend can also be referred to as an "alloy" when a single phase is obtained.

[00064] In one embodiment, powder composition blends of the invention include at least about 10 weight % based on total weight of the composition of at least one polymer other than the TPU. It has been found, for example, that a powder composition blend comprising about 10 weight % TPU and up to about 90 weight % polyvinyl chloride (PVC) based on total weight of the composition is useful in providing materials with improved properties. The use of PVC in powder composition blends of the invention provides a relatively cost-effective material with improved properties over PVC alone. When a powder composition blend is prepared according to one embodiment of the invention, the base TPU component is present in an amount of about 5 to about 50 weight % based on total weight of the composition. In progressively preferred embodiments, the base TPU component is present in amounts of about 10 to about 30 weight % or about 15 to about 25 weight % based on total weight of the composition. The remaining components include PVC and other optional components.

[00065] One particular component preferred for inclusion in certain embodiments of powder composition blends of the invention is a melt-processible rubber available from Advanced Polymer Alloys division of Ferro Corp. (Wilmington, DE) under the ALCRYN trade designation. Such melt-processible rubbers can be present in the compositions in an amount of about 5 to about 50 weight % based on total weight of the composition. In further embodiments, such a melt- processible rubber can be present in the compositions in an amount of about 10 to about 40 weight % based on total weight of the composition. In still further embodiments, such a melt-processible rubber can be present in the compositions in an amount of about 15 to about 30 weight % based on total weight of the composition. [00066] The combination of TPU and PVC in unique powder composition blends results in materials with improved modes of failure as compared to those materials consisting essentially of PVC. PVC typically exhibits a brittle failure mode, but blends of PVC and TPU were found to exhibit a more ductile mode of failure. It is preferred to use materials with ductile modes of failure in many applications. Passenger compartment air bag applications are one example of those applications where use of materials with increased ductility is desirable. When materials exhibiting brittle failure are used to prepare air bags, the air bags tend to shatter when used at lower temperatures (e.g., especially those temperatures less than about -4O⁰C). Thus, in order to effectively employ air bags in colder climates, improved materials have been desired.

[00067] Powder composition blends of the invention offer such improved materials. Compositions of the invention are capable of successfully passing rigorous tests imposed by vehicle manufacturers with respect to air bag materials. [00068] Formation Of Powder [00069] Powder compositions of the invention are prepared such that they have an average particle size and particle size distribution according to the desired use and processing method for articles prepared therefrom. A variety of particle sizes may be prepared. In one exemplary embodiment, powder compositions of the invention have an average particle size of about 80μm to about 300 μm. In a further embodiment, the average particle size is at least about lOOμm, or even at least about 200μm in still further embodiments.

[00070] Particle analysis can be performed using any suitable equipment and methods according to knowledge of those skilled in the art. In certain applications, the particle size distribution is preferably uni-modal, such as that distribution illustrated in FIGURE 1. According to the particle size distribution in FIGURE 1, 50% of the particles screened had a size of about 128μm or less and 95% of the particles screened had a size of about 253 μm or less. In other applications, the particle size distribution is preferably bi-modal, such as that distribution illustrated in FIGURE 2. According to the particle size distribution in FIGURE 2, 50% of the particles screened had a size of about 230 μm or less and 95% of the particles screened had a size of about 423 μm or less. The particle size distributions illustrated in FIGURES 1 and 2 were obtained using well known methods and particle analysis equipment available from Microtrac, Inc. of Montgomeryville, AL. [00071] Components of the composition are first mixed in proportional amounts selected according to the desired overall formulation and intended use. It is during the mixing of the base TPU that water may be optionally injected into the mixture in a minor amount sufficient (e.g., usually a trace amount of water will suffice for this purpose) to increase the MFI of the TPU when desired. [00072] While it may not be necessary to premix all of the composition' s components prior to transformation into a powder, those components that require such transformation are preferably mixed prior to forming a powder. Alternatively, although it is not desired due to efficiency, the composition can be formed by multiple mixing and powder-forming steps.

[00073] In order to obtain a substantially uniform mixture of the base TPU and optional components, mixing may occur in the presence of heat and/or pressure. For example, the components may be mixed in an extruder, exiting the extruder via a pelletizer. Once processed in this manner, the pellets so formed can be transformed into a powder of the desired particle size and distribution. [00074] In order to transform the mixed composition into a powder of the desired particle size and distribution, any suitable powder- forming technique can be used. For example, a powder can be prepared from the mixed composition using mechanical techniques such as cryogenic grinding or hammer milling. [00075] Note that a single pass through a cryogenic grinding process is generally not sufficient to prepare a powdered composition of the desired particle size distribution for later uses including the HVIF technique described further below. While other powder-forming techniques can be used and may be more efficient, cryogenic grinding followed by screening and recycling steps can be used to reach the desired particle size distribution. Also see U.S. Patent No. 5,597,586, which discloses a method for transformation of a composition into a useful powder-like form using underwater micropelletizing. In addition, U.S. Patent No. 5,654,102 discloses a method for transformation of a composition into microspheres of a size suitable for certain applications such as slush molding.

[00076] FIGURE 3 illustrates an exemplary embodiment of a process for preparation of powder compositions of the invention. Details and variations with respect to the steps and equipment illustrated therein are within the knowledge of those skilled in the art.

[00077] As shown in FIGURE 3, first a high intensity mixer 10 (e.g. , a

Henschel-type variable speed mixer, such as those available from the Japanese company, Mitsui Mike) operating at a temperature of about 12O⁰C to about 14O⁰C is provided for the initial mixing steps. The high intensity mixer 10 is loaded with a mixture 12 of base TPU and other components desired for the particular application (e.g., lubricants, flow agents, stabilizers, pigments, and the like) desired. Optionally, further other components 14 desired for the particular application are then added to high intensity mixer 10 after being pre-heated (e.g., in certain embodiments, plasticizer can be added after being pre-heated to a temperature of about 8O⁰C to about 9O⁰C).

[00078] The mixture is then transferred from the high intensity mixer 10 to a low intensity mixer 16 (e.g., a Henschel-type cooler mixer operating at a speed of about 110 rpm) that simultaneously cools the mixture. If a powder composition blend is being formed, the other polymer 18 (e.g., polyvinyl chloride) can be added to the mixture while being processed in the low intensity mixer 16. When the mixture reaches a temperature of about 5O⁰C it can be discharged to a hopper 20 for further processing to complete the dry blending operations 22.

[00079] From the hopper 20, the mixture is run through a screener 24 (e.g., a vibratory screener having a 10-mesh screen, such as a Sweco-type screener. Any oversize components 26 are discarded with the remaining components being then transferred to a receptacle 28 where they remain in the form of a dry powder until being transferred to an extruder 30 (e.g., a twin-screw extruder such as a Leistritz 27- millimeter co-rotating extruder having the designation MIC 27 GL/40D) for melt compounding (e.g., at a temperature of about 18O⁰C and a speed of about 350 rpm) followed by the remaining extrusion operations 32. Optionally, water can be injected into the extruder to help control MFI of the material as desired. After the material exits the extruder 30, it passes through a water cooler 34 and then to a pelletizer 36 (e.g., a strand pelletizer equipped with a trough, such as those available from the Conair Group Inc. of Pittsburgh, PA). The material exits the pelletizer 36 in the form of pellets 38.

[00080] The pellets 38 are then subjected to cryogenic grinding operations 40.

First, the pellets 38 are cooled in liquid nitrogen 42 and then transferred to an attrition mill 44 (e.g., such as cryogenic attrition mills available from Midwest Elastomers, Inc. of Wapakoneta, OH). From the attrition mill 44, the pellets are then run through a first cyclone separator 46 to a screener 48, which allows for transfer of particles of a desired dimension to a second cyclone separator 50. Oversize particles 52 are returned to the liquid nitrogen 42 for further milling. En route to the second cyclone separator 50 the screened composition can be heated using, for example, dry forced air. Finally, the resulting powder composition 54 exits the second cyclone separator 50 where it is stored until it is packaged or used for formation of an article prepared from the powder composition 54. [00081] Uses

[00082] TPU compositions of the invention can be used to form a variety of articles. Advantageously, compositions of the invention are capable of providing improved surface finishes on many articles prepared therefrom. For example, due to the relatively uniform and small particle size of certain embodiments of powder compositions of the invention, polymeric skins formed therefrom often have few surface imperfections as compared to those prepared from other compositions. [00083] As such, a first exemplary use of compositions of the invention involves high velocity impact fusion (HVIF). This technique facilitates formation of polymeric skins using formulations of the invention. In this embodiment utilizing HVIF techniques, the TPU powder composition preferably has an average particle size corresponding to the particle size distribution of FIGURE 1. Particles of smaller size typically result in waste as they are often not capable of reaching the target substrate during HVIF processing designed for use with particles of a predominantly large size, so their exclusion is preferred. It is preferred that the particle size distribution for compositions used in HVIF processes is relatively uni-modal. [00084] According to the HVIF technique, the composition is heated and then sprayed onto a mold surface to form an article. In one embodiment, the composition is heated to the point of melting using a hot nitrogen or oxygen environment. Once fluidized in this manner, the composition is directed toward a substrate (e.g., nickel- plated steel) maintained at approximately room temperature. Once the composition comes to rest upon the substrate, it cools to form the article. In an exemplary embodiment, the article is a continuous, solid film (e.g., a polymeric skin). In certain embodiments using the HVIF technique, the mold surface is textured in order to impart a desired surface finish to an article. For example, the mold surface may be textured to appear leathery when preparing articles such as instrument panels, armrests, headrests, door panels, and other items in passenger compartments of vehicles.

[00085] One exemplary commercial source of equipment useful for this HVIF technique is the Weidman Company, Inc. in Ft. Myers, Florida. Further details of one embodiment of this technique are described, for example, in U.S. Patent No. 5,285,967, which is assigned to the Weidman Company, Inc. and discusses high velocity oxygen fuel (HVOF) spraying techniques and associated equipment. As described therein, HVOF employs a continuous combustion procedure that produces exit gas velocities of up to about 1,200 - 1,500 meters/second (4,000 - 5,000 feet/second). To produce gas having this exit velocity, a fuel gas such as propylene or hydrazine and oxygen under high pressure at approximately 0.4 - 0.6 MPa (60 to 90 psi) is burned in an internal combustion chamber. Hot exhaust gases discharge from the combustion chamber through exhaust ports and expand into an extended nozzle where it meets with the powdered composition, which is fed into the nozzle with an inert carrier gas such as nitrogen and confined by the exhaust gas stream. The powdered composition melts therein and exits the nozzle in a high speed jet stream having a length of about 9 decimeters (36 inches) and a stream diameter of about 1.2 centimeters (1/2 inch). Utilizing this technique, a sufficiently dense coating of the composition is capable of being produced with properties superior to those obtained using other techniques.

[00086] Other uses of compositions of the invention for formation of articles involve conventional powder coating techniques including fluidized bed, electrostatic spray, and thermal spray techniques. Other such uses include conventional molding techniques such as slush molding and rotational molding.

[00087] According to the fluidized bed technique, heated metal parts are dipped in an aerated bed of the powdered composition. The powder melts on the heated part, resulting in a smooth continuous film encapsulating the metal. This process takes place in what is referred to as a "fluidized bed." The fluidized bed has three main sections: (1) a top powder hopper where the powder is held, (2) a porous plate that allows air to pass through, and (3) a sealed bottom air chamber. When pressurized air is blown into the air chamber, it passes through the plate and causes the powder to float or "fluidize". This fluidization allows the metal part to be coated and moved through the powder with little resistance during the dipping process. Alternatively, a cold substrate can be run over a bed of fluidized particles that are tribo-charged and, thus, cling to the substrate. The coated substrate can then be passed through a heated zone, or nip, to fuse the coating.

[00088] According to the electrostatic spray technique, the powdered composition is dispersed in an air stream and passed through a corona discharge field. In the corona discharge field, the powder acquires an electrostatic charge. The charged powder is attracted to and then deposited on the grounded substrate. The substrate, usually electrostatically coated at room temperature, is then placed in an oven where the powder melts and forms a coating.

[00089] Known thermal spray processes are characterized by their heating method. Those employing chemical combustion heating include powder flame spraying. Those employing electrical heating include plasma flame spraying. Of these processes, plasma flame spraying has taken a predominant role. [00090] Plasma flame spraying is a process whereby the deposition of a largely molten material is enabled by using a highly directional gas stream. Plasma, an ionized gas consisting of free electrons, positive ions, atoms and molecules, is used as a means of heating the powdered composition to a molten state at a high temperature (e.g., approximately 15,000⁰C) by using an electric arc. To generate the arc, a selected gas such as argon or nitrogen flows between an anode and cathode. Between the anode and cathode, an arc is generated in the gas flow, which heats and propels the composition to a substrate. Upon impinging the substrate, the composition heat- fuses to form a coating.

[00091] In contrast to the plasma flame spraying technique, conventional low velocity open atmosphere powdered flame spraying utilizes combustion as a means to heat the powder. The powdered composition, combustion air, and fuel are delivered to an open mixing combustion chamber where it ignites. Ignition of the fuel and gas mixtures melts the composition, which is then carried from the combustion chamber by the air so as to provide a coated substrate. Due to the lower velocity of the composition impinging upon the substrate in this method as compared to the HVIF technique described above, resulting coatings often have insufficient bond strength and does not lend itself to repeatable high production processes. [00092] Slush molding utilizes an open-end mold design for forming articles

(e.g., vehicle instrument panels). In this embodiment, the TPU powder composition preferably has a larger average particle size than that preferred for use with the HVIF technique. For example, compositions with an average particle size corresponding to the particle size distribution illustrated in FIGURE 2 can be used. In this embodiment, the particle size distribution of compositions used in this process need not be relatively uni-modal as is the case with those compositions used in the HVIF process described above. Rather, bi-modal particle size distributions can be used, such as those obtained from cryogenic grinding of the TPU. [00093] Rotational molding is another technique for forming articles (e.g., armrests and headrests in passenger compartments of vehicles as well as other objects such as recreational balls). As compared to slush molding, the rotational molding process operates on one rotational axis using a closed-mold design. Further, although a bi-modal particle size distribution can also be used when rotational molding, the distribution is typically of a larger average particle size than that used for slush molding.

[00094] According to one of the above or another suitable method for formation of articles utilizing powdered formulations, articles are formed from TPU and TPU powder composition blends of the invention. By integrating improved powder compositions of the invention with processing techniques such as the HVIF technique, superior articles are made possible. Such articles are useful for not only satisfying needs of industries such as those involving manufacture of polymeric articles used in passenger compartments of vehicles.

[00095] Further embodiments and applications of the invention are described in the following non-limiting examples.

EXAMPLES [00096] Example 1

[00097] A base TPU was obtained from a commercial source under the trade designation ELASTOLLAN LJ 56/187(BASF Corp. of Wyandotte, MI). When tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg, the MFI of the base TPU was measured to be 55 g/10 min. When tested according to ASTM D1238 at the lower temperature of 17O⁰C and the same weight of 2.16 kg, the MFI of the base TPU was measured to be 27 g/10 min.

[00098] In a high intensity mixer, the base TPU was mixed with an internal lubricant (mono- and di-stearyl acid phosphate, AX-71, available from Amfine Chemical of Mie, Japan), and a pigment (carbon black, available from Cabot Corp. of Boston, MA, under the REGAL BLACK trade designation). The high intensity mixer was operated at a temperature of about 12O⁰C to about 14O⁰C. The mixture was then transferred from the high intensity mixer to a low intensity mixer operating at a speed of about 110 rpm to mix and simultaneously cool the mixture. When the mixture reached a temperature of about 5O⁰C, it was discharged to a hopper and then run through a screener. Screened particles were then fed to a twin-screw extruder operating a temperature of about 18O⁰C and a speed of about 350 rpm. After exiting the extruder, the mixture was passed through a water cooler and then to a pelletizer to form pellets. The pellets were then subjected to cryogenic grinding operations. [00099] Once the powder was formed, a flow agent (PS-200, available from

Glassven CA. , a Venezuelan company, under the PIROSIL trade designation) was mixed with the powder in an amount of 0.15% based on total weight of the composition. In the composition thus formed, the amount of base TPU was 99.05%, the amount of internal lubricant was 0.30%, and the amount of pigment was 0.50%, all weight percentages based on total weight of the composition. [000100] Example 2 [000101] In a high intensity mixer, a base TPU (ELASTOLLAN LJ 56/187, available from BASF Corp. of Wyandotte, MI) was mixed with an internal lubricant (mono- and di-stearyl acid phosphate, AX-71, available from Amfine Chemical of Mie, Japan), and a pigment (carbon black dispersion, available from PolyOne Corp. of Avon Lake, OH, under the STAN-TONE HCC-20327 BLACK trade designation). The mixture was processed to form a powder composition as described with reference to Example 1. In the powder composition thus formed, the amount of base TPU was 98.2%, the amount of internal lubricant was 0.2%, and the amount of pigment was 1.6%, all weight percentages being based on total weight of the composition. [000102] Example 3

[000103] The process described with reference to Example 1 and FIGURE 3 was used to form a powder composition blend. The powder composition blend was formed from 30.0% base TPU (ELASTOLLAN LJ 56/187, available from BASF Corp. of Wyandotte, MI), 0.1% internal lubricant (mono- and di-stearyl acid phosphate, AX-71, available from Amfine Chemical of Mie, Japan), 33.3% polyvinyl chloride resin suspension (SUSP RESIN 200F (DPK), available from Oxy vinyls Corp. of Deer Park, TX), 1.4% mixed stabilizer (CPS 507, available from Amfine Chemicals of Hopkinsville, KY), 0.1% fatty acid ester (LS-10, available from Amfine Chemicals of Mie, Japan), 0.9% phosphite stabilizer (CPL-1551 D, available from Amfine Chemical of Hopkinsville, KY), 2.8% pigment dispersion (VM6432 9779 MD GRAY MB, available from PolyOne Corp. of Avon Lake, OH), 28.1% n-octyl trimellitate plasticizer (SYNPLAST NOTM ELECTRICAL, available from Synergistics of St. Remi, Canada), and 3.3% polyvinyl chloride resin dispersion (VINNOLIT P70, available from Vinnolit of Ismaning, Germany). All weight percentages are based on total weight of the composition. [000104] Example 4

[000105] The process described with reference to Example 1 and FIGURE 3 was used to form a powder composition blend. The powder composition blend was formed from 30.0% base TPU (ELASTOLLAN LJ 56/187, available from BASF Corp. of Wyandotte, MI), 0.1% internal lubricant (mono- and di-stearyl acid phosphate, AX-71, available from Amfine Chemical of Mie, Japan), 32.5% polyvinyl chloride resin suspension (SUSP RESIN 200F (LVL), available from Oxy vinyls Corp. of Deer Park, TX), 0.1% mixed stabilizer (CPS 507, available from Amfine Chemicals of Hopkinsville, KY), 0.1% fatty acid ester (LS-10, available from Amfine Chemicals of Mie, Japan), 0.7% phosphite stabilizer (CPL-1551 D, available from Amfine Chemical of Hopkinsville, KY), 1.6% pigment dispersion (0928189 642H V DK PEWTER MB, available from PolyOne Corp. of Avon Lake, OH), 30.2% n-octyl trimellitate plasticizer (SYNPLAST NOTM ELECTRICAL, available from Synergistics of St. Remi, Canada), and 3.9% polyvinyl chloride resin dispersion (VINNOLIT P70, available from Vinnolit of Ismaning, Germany). All weight percentages are based on total weight of the composition.

[000106] Various modifications and alterations of the invention will become apparent to those skilled in the art without departing from the spirit and scope of the invention, which is defined by the accompanying claims. It should be noted that steps recited in any method claims below do not necessarily need to be performed in the order that they are recited. Those of ordinary skill in the art will recognize variations in performing the steps from the order in which they are recited.

Claims

1. A thermoplastic powder composition suitable for formation into an article using high velocity impact fusion, the powder composition comprising: at least one thermoplastic polyurethane having a melt flow index of at least about 8 g/10 min when tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg; at least one internal lubricant in an amount of up to about 5 weight % based on total weight of the composition; and optionally, at least one flow agent, wherein the powder has a uni-modal particle size distribution.

2. The thermoplastic powder composition of claim 1, wherein the thermoplastic polyurethane comprises aliphatic thermoplastic polyurethane.

3. The thermoplastic powder composition of claim 1, wherein the thermoplastic polyurethane comprises aromatic thermoplastic polyurethane.

4. The thermoplastic powder composition of claim 1, wherein the thermoplastic polyurethane comprises polyether-based thermoplastic polyurethane.

5. The thermoplastic powder composition of claim 1, wherein the thermoplastic polyurethane comprises polyester-based thermoplastic polyurethane.

6. The thermoplastic powder composition of claim 1, wherein the thermoplastic polyurethane comprises aromatic polyether-based thermoplastic polyurethane.

7. The thermoplastic powder composition of claim 1, wherein the thermoplastic polyurethane comprises aliphatic polyester-based thermoplastic polyurethane.

8. The thermoplastic powder composition of claim 1, wherein the composition comprises about 0.01 to about 1.0 weight % mono- and di-stearyl acid phosphate based on total weight of the composition.

9. The thermoplastic powder composition of claim 1, wherein the composition is essentially free of components prone to blooming migration in articles prepared therefrom.

10. The thermoplastic powder composition of claim 1, further comprising at least one component selected from heat stabilizers, light stabilizers, pigments, antioxidants, plasticizers, fillers, and mattening agents.

11. An article prepared from the thermoplastic powder composition of claim 1.

12. The article of claim 11, wherein the article comprises a polymeric skin subcomponent of a further article for a passenger compartment of a vehicle.

13. The article of claim 12, wherein the further article is selected from an instrument panel, door panel, armrest, headrest, center console, and an air bag for a passenger compartment of a vehicle.

14. A powder composition blend comprising at least one thermoplastic polyurethane and at least one other polymer.

15. The powder composition blend of claim 14, wherein the other polymer comprises greater than about 10 weight % of the total composition.

16. The powder composition blend of claim 14, wherein the other polymer comprises polyvinyl chloride.

17. The powder composition blend of claim 14, wherein the other polymer comprises polyvinyl chloride in an amount up to about 90 weight % of the total composition.

18. The powder composition blend of claim 14, further comprising a melt- processible rubber.

19. The powder composition blend of claim 14, wherein the composition comprises at least one thermoplastic polyurethane in an amount of about 5 to about 50 weight % of the total composition.

20. The powder composition blend of claim 14, wherein the composition comprises at least one thermoplastic polyurethane in an amount of about 10 to about 30 weight % of the total composition.

21. The powder composition blend of claim 14, wherein the composition comprises at least one thermoplastic polyurethane in an amount of about 15 to about 25 weight % of the total composition.

22. The powder composition blend of claim 14 having a uni-modal particle size distribution.

23. The powder composition blend of claim 14 having a bi-modal particle size distribution.

24. An article prepared from the powder composition blend of claim 14.

25. The article of claim 24, wherein the article comprises a polymeric skin subcomponent of a further article for a passenger compartment of a vehicle.

26. The article of claim 25, wherein the further article is selected from an instrument panel, door panel, armrest, headrest, center console, and an air bag for a passenger compartment of a vehicle.

27. The article of claim 25, wherein the further article comprises an air bag for a passenger compartment of a vehicle.

28. A process for preparing the thermoplastic powder composition of claim 1, comprising steps of: providing the thermoplastic polyurethane; mixing the thermoplastic polyurethane with one or more optional components; and transforming the thermoplastic polyurethane and optional components into the powder having the uni-modal particle size distribution.

29. The process of claim 28, wherein the thermoplastic polyurethane and optional components are transformed into the powder using cryogenic grinding, screening, and recycling steps.

30. The process of claim 28, further comprising reducing molecular weight of the thermoplastic polyurethane by injecting water into an extruder at a position where the thermoplastic polyurethane is molten in order to increase melt flow index of the thermoplastic polyurethane to at least about 8 g/10 min when tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg.

31. A process for preparing an article from the thermoplastic powder composition of claim 1, comprising steps of: providing the thermoplastic powder composition; and forming the article from the thermoplastic powder composition using a high velocity impact fusion technique.

32. The process of claim 31, wherein an external mold release agent is not utilized to form the article.

33. A process for preparing the powder composition blend of claim 14, comprising steps of: providing the thermoplastic polyurethane; mixing the thermoplastic polyurethane with the other polymer and optional components to form a blend; and transforming the mixture into a powder having a predetermined particle size distribution.

34. A process for preparing an article from the powder composition blend of claim 14, comprising steps of: providing the powder composition blend; and forming the article from the thermoplastic powder composition blend.

35. The process of claim 34, wherein the article is formed using a high velocity impact fusion, fluidized bed powder coating, electrostatic spray, thermal spray, slush molding, or rotational molding technique.

36. A thermoplastic powder composition suitable for formation into an article using slush molding, the powder composition comprising: at least one thermoplastic polyurethane having a melt flow index of at least about 8 g/10 min when tested according to ASTM D1238 at 19O⁰C and a weight of 2.16 kg; at least one internal lubricant in an amount of up to about 5 weight % based on total weight of the composition; and optionally, at least one flow agent, wherein the powder has a bi-modal particle size distribution.

37. An article prepared from the thermoplastic powder composition of claim 36.

38. A process for preparing an article from the powder composition of claim 36, comprising steps of: providing the powder composition; and forming the article from the thermoplastic powder composition.