Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L53/00—Compositions of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
  • C08L53/02—Compositions of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers of vinyl-aromatic monomers and conjugated dienes
  • C08L53/025—Compositions of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers of vinyl-aromatic monomers and conjugated dienes modified
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F297/00—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer
  • C08F297/02—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer using a catalyst of the anionic type
  • C08F297/04—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer using a catalyst of the anionic type polymerising vinyl aromatic monomers and conjugated dienes

Definitions

• This invention relates to elastomeric polymer compositions that can be extruded into fibers or films. More specifically, the invention relates to new high vinyl styrene-diene block copolymer compositions for use in making film or spun bond fiber for elastic nonwovens laminates.
• Extrudable elastomeric compositions which can be easily compression molded or melt blown into elastic fibers or films having low stress relaxation, low hysteresis, and high recoverable energy are known.
• the elastomeric fibers or films are useful in making a variety of applications such as diaper waistbands and non-woven fabrics.
• thermoplastic elastomer compositions have been developed for making film or spun bond fiber nonwovens laminate for personal hygiene applications.
• U.S. Patent 4,789,699 disclosed such compositions based on styrene- ethylene/butylene-styrene (SEBS) polymers the incorporate additional tackifier and polyolefin resins.
• SEBS styrene- ethylene/butylene-styrene
• One of the drawbacks of this composition was the relatively poor elastic recovery performance.
• U.S. Patent No. 5,093,422 discloses composition based on styrene-propylene/ethylene styrene (SEPS) polymers which are said to improve the elastic properties of the materials. However, the flow behavior of these compositions was reduced.
• SEPS styrene-propylene/ethylene styrene
• 5,332,613 discloses a composition based on styrene-ethylene/propylene-styrene-ethylene/propylene (SEPSep) four- block polymers as a way to balance the hysteresis and flow performance.
• SEPSep styrene-ethylene/propylene-styrene-ethylene/propylene
• SEBS elastomeric block copolymers and SEPS elastomeric block copolymers have been blended as discussed above to form extrudable elastomeric compositions which can be formed into elastic fibers or films. While the additives, tackifying resins or polyolefins, improve the extrusion properties of the compositions and the processing and/or bonding properties of the elastic fibers or films, such additives have an adverse affect on the elastic properties of the resulting fiber or film, especially at temperatures above 25°C.
• the present invention provides an elastomeric composition which is useful as an elastic film and fiber grade compound.
• These compositions contain at least one SEBS block copolymer having a vinyl content of 60 percent or greater and a number average molecular weight of 40,000 to 110,000, preferably 60,000 to 100,000, and a styrene block molecular number average weight of 5,000 to 15,000.
• the composition will comprise from 60 to 85 percent by weight of the block copolymer, from 5 to 25 percent by weight of a tackifying resin, and from 10 to 35 percent by weight of a polyethylene.
• an elastic film grade compound which does not contain a tackifing resin.
• the composition is comprised of from 5 to 35 percent by weight of a polyethylene and the balance is comprised of the block copolymer described above.
• a third embodiment of this invention provides another elastic film grade compound.
• This compound also contains no tackifying resin. It is comprised of from 2 to 60 percent by weight of a metallocene polyethylene elastomer polymer and the balance is the block copolymer described above.
• vinyl content refers to the fact that a conjugated diene is polymerized via 1 ,2-addition (in the case of butadiene - it would be 3,4-addition in the case of isoprene). Although a pure "vinyl" group is formed only in the case of 1 ,2-addition polymerization of 1 ,3-butadiene, the effects of 3,4-addition polymerization of isoprene (and similar addition for other conjugated dienes) on the final properties of the block copolymer will be similar.
• the term "vinyl” refers to the presence of a pendant vinyl group on the polymer chain.
• the extrudable elastomeric composition of the present invention is an improvement of the extrudable compositions described in United States Patents Nos. 4,970,259, 5,093,422, and 5,332,613 which descriptions are incorporated by reference herein.
• the known compositions include one or more styrenic block copolymers, typically an SEBS or an SEPS or an SEPSep elastomeric block copolymer which is produced by hydrogenating a polystyrene-polybutadiene- polystyrene or polystyrene-polyisoprene-polystyrene or polystyrene-polyisoprene- polystyrene-polyisoprene block copolymer.
• the SEBS block copolymers which were specifically discussed and utilized in the above patents all had vinyl contents in the "normal" range of 35 to 55 percent by weight.
• the compositions contain at least one hydrogenated polystyrene-polybutadiene-polystyrene block copolymer (S-EB-S) having a vinyl content in the saturated block of polybutadiene of at least 60 percent by weight and preferably from 60 to 85 percent by weight in comparison to the conventional block copolymers used to make elastomeric films and fibers commercially and described in the above patents.
• S-EB-S hydrogenated polystyrene-polybutadiene-polystyrene block copolymer
• the S-EB-S block copolymer may be blended with other hydrogenated block copolymers, such as the SEPS or the SEPSep elastomeric block copolymers, or the butadiene may be co-polymerized with other conjugated dienes, such as isoprene, in amounts that retain improved elastomeric properties.
• the styrenic block copolymers have at least two poly(monoalkenylarene) blocks, preferably two polystyrene blocks, separated by a saturated block of a poly(conjugated diene), preferably a saturated polybutadiene.
• the preferred block copolymers comprise two polystyrene blocks, at least one block having a number average molecular weight from 5,000 to 15,000, and one saturated polybutadiene midblock, each having a number average molecular weight from 30,000 to 85,000.
• the saturated polybutadiene blocks preferably have at least 60 percent by weight 1 ,2-configuration (vinyl content) and preferably from 60 to 85 percent.
• the total number average molecular weight of the block polymer is from 40,000 to 110,000, preferably 60,000 to 100,000, and the block copolymers preferably have an average polystyrene content from 12% to 25% by weight.
• polymers may be prepared using free-radical, cationic and anionic initiators or polymerization catalysts. Such polymers may be prepared using bulk, solution or emulsion techniques. In any case, the polymer containing at least ethylenic unsaturation will, generally, be recovered as a solid such as a crumb, a powder, a pellet, or the like.
• conjugated diolefin polymers and copolymers of conjugated diolefins and alkenyl aromatic hydrocarbons are prepared by contacting the monomer or monomers to be polymerized simultaneously or sequentially with an organoalkali metal compound in a suitable solvent at a temperature within the range from about -150°C to about 300°C, preferably at a temperature within the range from about 0°C to about 100°C.
• organoalkali metal compound in a suitable solvent at a temperature within the range from about -150°C to about 300°C, preferably at a temperature within the range from about 0°C to about 100°C.
• organolithium compounds having the general formula:
• R is an aliphatic, cycloaliphatic, aromatic, or alkyl-substituted aromatic hydrocarbon radical having from 1 to about 20 carbon atoms; and n is an integer of 1 to 4.
• anionic initiators can be used to prepare diblocks of polystyrene-polydiene having a reactive ("live") chain end on the diene block which can be reacted through a coupling agent to create, for example, (S-I) X Y or (S-B) X Y structures wherein x is an integer from 2 to about 30, Y is a coupling agent, I is isoprene, B is butadiene and greater than 65 percent of S-l or S-B diblocks are chemically attached to the coupling agent.
• Y usually has a molecular weight which is low compared to the polymers being prepared and can be any of a number of materials known in the art, including halogenated organic compounds; halogenated alkyl silanes; alkoxy silanes; various esters such as alkyl and aryl benzoates, difunctional aliphatic esters such as dialkyl adipates and the like; polyfunctional agents such as divinyl benzene (DVB) and low molecular weight polymers of DVB.
• the coupling agent being of low molecular weight, does not materially affect the properties of the final polymer.
• DVB oligomer is commonly used to create star polymers, wherein the number of diene arms can be 7 to 20 or even higher.
• the styrenic block copolymers must be hydrogenated.
• the hydrogenation or selective hydrogenation of the polymer may be accomplished using any of the several hydrogenation processes known in the prior art.
• the hydrogenation may be accomplished using methods such as those taught, for example, in U.S. Patent Nos. 3,494,942; 3,634,594; 3,670,054; 3,700,633; and Re. 27,145, the disclosure of which patents are incorporated herein by reference.
• the methods known in the prior art and useful in the present invention for hydrogenating polymers containing ethylenic unsaturation and for hydrogenating or selectively hydrogenating polymers containing aromatic and ethylenic unsaturation involve the use of a suitable catalyst, particularly a catalyst or catalyst precursor comprising an iron group metal atom, particularly nickel or titanium or cobalt, and a suitable reducing agent such as an aluminum alkyl.
• a suitable catalyst particularly a catalyst or catalyst precursor comprising an iron group metal atom, particularly nickel or titanium or cobalt
• a suitable reducing agent such as an aluminum alkyl.
• the amount of ethylenic unsaturation remaining after hydrogenation is typically less than 20%.
• the level of saturation achieved by hydrogenation is desirably greater than about 95%.
• the level of saturation achieved by hydrogenation is desirably greater than about 98%. More desirably, the level of saturation achieved by hydrogenation is greater than about 99%.
• the hydrogenation will be accomplished in a suitable solvent at a temperature within the range from about 20°C to about 100°C and at a hydrogen partial pressure within the range from about 100 psig (8 bar) to about 5,000 psig (350 bar), preferably about 100 psig (8 bar) to 1 ,000 psig (70 bar).
• Catalyst concentrations within the range from about 10 ppm (wt) to about 500 ppm (wt) of metal based on total solution are generally used and contacting at hydrogenation conditions is generally continued for a period of time within the range from about 60 to about 240 minutes.
• the hydrogenation catalyst and catalyst residue will, generally, be separated from the polymer.
• compositions of the present invention may include from 5 to 35 percent by weight of one or more polyolefins.
• the polyolefins which may be utilized in the extrudable -composition must be polyolefins which, when blended with the elastomeric block copolymer or a mixture of elastomeric block copolymers and subjected to an appropriate combination of elevated pressure and elevated temperature conditions, is extrudable, in blended form, with the elastomeric block copolymer or a mixture of elastomeric block copolymers.
• preferred polyolefin materials include low molecular weight low density polyethylene with a density of less than 0.92 grams per cubic centimeter and a melt index greater than 30 grams/10 minutes, and linear low density polyethylene, metallocene linear low density polyethylene, various ethylene copolymers, such as low vinyl acetate polyethylene, ethylene methyl acrylate copolymer, ethylene acrylic acid, ethylene methacrylic acid resins etc. Blends of two or more of the polyolefins may be utilized.
• PE NA 601-04 also referred to herein as PE NA 601
• Information obtained from Equistar Chemical states that PE NA 601 is a low molecular weight, low density polyethylene for application in the areas of hot melt adhesives and coatings.
• PE NA 601 exhibits following key characteristics: (1) a density of 0.903 grams per cubic centimeter when measured in accordance with ASTM D 1505; and (2) an equivalent Melt index of 2,000 grams per 10 minutes when measured in accordance with ASTM D 1238.
• the above block copolymers are blended with a metallocene polyolefin having a density from 0.86 to 0.91 , a molecular weight distribution less than 3, and from 8% to 30% by weight of an ⁇ - olefin comonomer having from 4 to 12 carbon atoms, preferably from 4 to 8 carbon atoms.
• the metallocene polyolefins are polyolefins produced with a metallocene catalyst as described in United States Patents No. 5,322,728 and 5,272,236 which are descriptions are incorporated by reference herein.
• Such elastomeric polyolefins are available from DuPont Dow Elastomers under the trademark ENGAGE (ethylene/octene copolymers), from Dow Chemical Company under trademark AFFINITY, and from Exxon Chemical Company under the trademark EXACT (ethylene/butene copolymers).
• the metallocene polyolefins have low crystallinity when ethylene is copolymerized with from 8% to 30% by weight of an ⁇ -olefin comonomer having from 4 to 12 carbon atoms.
• tackifying resins can be used in at least one of the embodiments of the present invention.
• the purpose of the tackifying resin is to allow elastomeric film or fiber to act as a pressure sensitive adhesive, e.g., to allow elastomeric film or fiber to bond to another web or layer of material.
• various tackifying resins are known, and are discussed, e.g., in U.S Patent Nos. 4,789,699; 4,294,936; and 3,783,072, the contents of which, with respect to the tackifier resins, are incorporated herein by reference.
• Any tackifier resin can be used which is compatible with the elastomeric polymer and the polyolefin, and can withstand the high processing (e.g., extrusion) temperatures.
• hydrogenated hydrocarbon resins are preferred tackifying resins, because of their better temperature stability.
• the following paragraphs disclose information on three specific tackifying resins, two of which (REGALREZ® and ARKON®P series tackifiers) are examples of hydrogenated hydrocarbon resins, and the ZONATACO501 Lite is a terpene hydrocarbon.
• the present invention is not limited to use of such three tackifying resins, and other tackifying resins which are compatible with the other components of the composition and can withstand the high processing temperatures, and can achieve the objectives of the present invention, can also be used.
• REGALREZ® hydrocarbon resins a product of Hercules, Incorporated, are fully hydrogenated ⁇ -methylstyrene, low molecular weight hydrocarbon resins, produced by polymerization and hydrogenation of pure monomer hydrocarbon feed stocks.
• Grades 1094, 3102, 6108, and 1126 are highly stable, light-colored low molecular weight, nonpolar resins suggested for use in plastics modification, adhesives, coatings, sealants, and caulks.
• the resins are compatible with a wide variety of oils, waxes, alkyds, plastics, and elastomers and are soluble in common organic solvents.
• ZONATAC®501 Lite resin a product of Arizona Chemical Co., has a softening point of 105°C, a Gardner color (50% in heptane) of 1 — and a Gardner color neat
• APHA color 70) a specific gravity (25°/25°C) of 1.02 and a flash point (closed cup, °F) of 480°F.
• a composition according to the present invention is provided as an elastic fiber grade compound.
• This composition comprises from 60 to 85 percent by weight of the above-described high vinyl content block copolymer, from 5 to 25 percent by weight of one of the above-described tackifying resins, and from 10 to 35 percent by weight of one of the above-described polyethylene resin.
• These compounds show excellent hysteresis recovery and good stress relaxation properties at body temperature. Increasing the vinyl content improves both of these properties as compared to the same polymer with a lower vinyl content. Additionally, these compounds exhibit improved melt flow characteristics and elasticity over compounds comprising similar polymers with lower vinyl contents.
• a composition which is a low molecular weight, low density polyethylene containing film compound.
• This compound does not contain any tackifying resin in order to minimize the softening effect of the tackifying resin. It will comprise from 15 to 35 percent of the low molecular weight, low density polyethylene material described above and the balance will be comprised of the high vinyl block copolymer described above. Within this composition range, these compounds exhibit improved elastic behavior and improved melt flow compared to compounds made from a similar polymer with a lower vinyl content. If the amounts of low molecular weight, low density polyethylene is increased to 50 percent, the compatibility of the high vinyl block copolymer and the polyethylene is poor. Also, such compounds exhibit poor tensile elongation and cannot sustain the stress relaxation test.
• another film grade compound is provided.
• This compound also contains no tackifying resin and it contains a metallocene elastomer polymer which is used instead of the low molecular weight, low density polyethylene or the combination of tw.
• This composition will contain from 2 to 60 percent by weight of the metallocene polyolefin and the balance is comprised of the high vinyl block copolymer described above. The compatibility of these polymers within this composition range is good. The blends are homogeneous and they exhibit excellent elastic properties even at the 50/50 blend ratio.
• extrudable elastomeric composition used to form the elastic sheet
• extrudable elastomeric composition is not limited thereto, and can include other components not adversely affecting the extrudable elastomeric composition attaining the stated objectives.
• Exemplary materials which could be. used as additional components would include, without limitation, pigments, antioxidants, stabilizers, surfactants, waxes, flow promoters, solvents, particulates, and materials added to enhance processability and pellet handling of the composition.
• elastic is used herein to mean any material which, upon application of a biasing force, is stretchable, that is, elongatable at least about 60 percent (i.e., to a stretched, biased length which is at least about 160 percent of its relaxed unbiased length) and which, will recover at least 55 percent of its elongation upon release of the stretching, elongating force.
• a hypothetical example would be a one (1 ) inch sample of a material which is elongatable to at least 1.60 inches (4.06 cm) and which, upon being elongated to 1 .60 inches (4.06 cm) and released, will recover to a length of not more than 1 .27 inches (3.23 cm).
• stress relaxation refers to the percent loss of tension or load between the maximum load or force encountered after elongating an elastic material at a specified rate of extension to a predetermined length (or the load or force measured at some initial length) and the remaining load or force measured after the sample has been held at that length for a specified period of time, for example, from about 10 minutes to about 30 minutes.
• stress relaxation is expressed as a percentage loss of the initial load encountered at a specified extension of an elastic material.
• the stress relaxation is determined by calculating the difference between the initial maximum load measured after elongating an elastic material at a rate of 20 inches (50.8 cm) per minute to an elongation of 160 percent (i.e., to 260 percent of the material's initial length) and the remaining load measured after that sample was held at that length for 30 minutes divided by the initial maximum load at that length. Testing may be performed on an Instron Model 5565 Universal Test Machine using ASTM microtensile specimens.
• tensile strength refers to the resistance of an elastic material to being elongated as determined in accordance with ASTM 412 Method using microtensile specimens that are cut from films. Films formed from a blend of an elastomeric block copolymer and other materials such as, for example, a polyolefin (metallocene and/or crystalline), a tackifier, and/or an extending oil were compression molded. Tensile testing may be performed on an Instron Model 5565 Universal Test Machine.
• the term "recoverable energy” refers to the energy stored by an elastic material when it is elongated to a specified length. Recoverable energy is measured utilizing a tensile testing apparatus such as, for example, an Instron Model 5565 Universal Test Machine by elongating a sample of an elastic material sample at 1 inch/minute to 150 percent elongation (i.e., to 250 percent of the material's initial relaxed length) and cycling back to zero load for 1 hysteresis loop. The percent recoverable energy is determined by dividing the area under the retraction curve of the first hysteresis loop by the area under the elongation curve of the first hysteresis loop and then multiplying by 100.
• a tensile testing apparatus such as, for example, an Instron Model 5565 Universal Test Machine
• the "number average molecular weight" was determined utilizing gel permeation chromatography techniques for linear anionic polymers. All molecular weights are measured prior to hydrogenation which will increase the molecular weights by a small amount.
• the molecular weights of linear polymers or unassembled linear segments of polymers such as mono-, di-, triblock, etc., arms of star polymers before coupling are conveniently measured by Gel Permeation Chromatography (GPC), where the GPC system has been appropriately calibrated.
• the polymer is essentially monodisperse (weight average molecular weight/number average molecular weight ratio approaches unity), and it is both convenient and adequately descriptive to report the "peak" molecular weight of the narrow molecular weight distribution observed. Usually, the peak value is between the number and the weight average.
• the peak molecular weight is the molecular weight of the main species shown on the chromatograph.
• the weight average molecular weight should be calculated from the chromatograph and used.
• styrene-divinyl benzene gels or silica gels are commonly used and are excellent materials. Tetrahydrofuran is an excellent solvent for polymers of the type described herein.
• a refractive index detector may be used.
• SEBS block copolymers of varying 1 ,2-vinyl content were made for these experiments.
• the conventional SEBS polymers of standard vinyl content (38 to 45 percent) were synthesized with diethylether as the structure modifier.
• the higher vinyl content polymers were synthesized with 1 ,2-diethoxy propane as the structure modifier.
• the first group of polymers, which are described in Table I, consists of SEBS polymers with about 100,000 overall total number average molecular weight, 13 to 21 percent polystyrene content, and vinyl contents ranging from 38 to 78 percent.
• the referenced conventional SEBS polymer (vinyl content of 38 percent) is typically used in high performance elastic SEBS polymer blends for film and fibers applications.
• the compound samples were prepared by melt blending the raw ingredients in a small Brabender Kneader at 400°F (204°C). Test samples were compression molded into 25 mil, 4 in. (10.2 cm) by 4 in. (10.2 cm) rectangular plaques at 380°F (193°C). ASTM micro tensile test specimens were die cut from the test plaques.
• the stress-strain properties of the pressed films were determined in accordance with ASTM D-412 utilizing a Constant Rate of Extension Tester, Instron Model 5565 Universal Testing Instrument. Each sample was placed lengthwise in jaw faces, with a jaw span of 0.75 inches (1.9 cm). The Instron Model 5565 Universal Test Instrument crosshead speed was set at 2 inches per minute for the first series of tests measuring the Stress-Strain properties. In addition, stress relaxation and hysteresis tests were measured using the Instron Model 5565 Universal Test Machine and determined as previously described. The specimens were cut orthogonally and the results were reported based on the average of both directions.
• Table I lists the characteristics and physical properties of the three polymers which were used to make the compounds which are evaluated in Tables II and III. It can be seen that the melt flow of the higher vinyl polymers is significantly higher than that of the standard vinyl content SEBS block copolymer and the rubber moduli of the higher vinyl polymers are lower than the referenced polymer (Polymer A). The elastic recovery behavior of the higher vinyl polymers is significantly better than the reference polymer while their stress relaxation properties at body temperature remain unchanged.
• Elastic fiber grade compounds containing the SEBS polymers of Table I were made and their corresponding physical properties are shown in Table II.
• Two types of elastic film formulations were used in this example.
• the first type of formulation (compounds 1 , 2 and 3 in Example 1 , Table II) contains SEBS block copolymer, tackifying resin, and a low density polyethylene resin.
• the polyethylene resin used was Equistar NA 601-04 which is described in detail above. This type of compound also exhibits hot melt adhesive behavior with the plasticization of the midblock by the tackifying resin. These compounds show excellent hysteresis recovery and good stress relaxation properties at body temperature. Increasing the vinyl content in the midblock improves both the hysteresis recovery and the stress relaxation.
• the second type of compounds described in Table II are binary blends of SEBS block copolymer and the same low density polyethylene resin used above.
• the compounds were prepared with SEBS/PE blend ratios of 85/15, 70/30, and 50/50 levels. The results are shown in Table II (Example 2, compounds 4 to 16).
• the high vinyl polymer compounds exhibit improved elastic behavior and improved melt flow compared to compounds from the reference polymer.
• the compatibility of the high vinyl SEBS polymer with low molecular weight, low density polyethylene is poor at the higher polyethylene content.
• the 50/50 blend exhibited poor tensile elongation and could not sustain the stress relaxation test.
• blends of high vinyl polymers B and C, formulation 12, 13, 17 and 18, exhibit better flow than formulations 7 and 8 made with "normal" vinyl polymer A while maintaining equivalent or better recoverable energy, permanent set and stress relaxation.

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