Patent Application
20130137331
Polypropylene polymers and polymer blends are well known in the art for their usefulness in the manufacture of nonwoven meltblown fabrics. Such fabrics have a wide variety of uses, such as in medical and hygiene products, clothing, filter media, and sorbent products, including those designed to absorb water, oil, and other chemicals. An important aspect of these fabrics, particularly in sorbent applications, is the fabric's loft, or thickness at a particular basis weight, with a higher loft being more desirable. Also desirable is a fabric with minimal roping (i.e., poor fiber separation) and linting.
Previously, such propylene-based nonwoven fabrics were prepared in melt blown processes using Ziegler-Natta catalyzed polypropylene granules coated with peroxide. The addition of peroxide serves to vis-break the propylene polymer, resulting in higher melt flow rates and narrower molecular weight distributions desirable for melt blown applications. Such peroxide coating also has drawbacks, however, such as an increase in the complexity and expense of the melt blowing process and the formation of decomposition byproducts, making the addition of peroxide undesirable.
Metallocene catalyzed propylene-based polymers are also known in the art and have been used to form meltblown fabrics. See, for example, U.S. Pat. Nos. 6,010,588, 7,081,299, and 7,319,122, which are incorporated herein by reference. While propylene-based polymers having high melt flow rates and narrow molecular weight distributions have been prepared with such single site catalysts, thus having the advantage of not requiring post reactor treatment (such as peroxide coating), those polymers have not resulted in fabrics exhibiting the loft and resistance to roping desired for certain absorbent and other applications. One possible way to increase the loft of a fabric is to use a water quench to cool the molten fibers of the fabric. This is undesirable too, however, because the high levels of water quench sometimes needed to produce satisfactory loft result in an excessive level of residual water in the fabric.
It would be desirable, then, to develop a propylene-based polymer composition that produces meltblown fabrics with high loft and resistance to roping without requiring post reactor treatment and minimizing water quenching. The present invention accomplishes these goals by blending a small amount of a propylene-based polymer having a lower melt flow rate or a higher level of isotacticity with a metallocene-catalyzed propylene-based polymer having a high melt flow rate. Nonwoven fabrics produced from the polymer blends of the invention have high loft and good resistance to roping and linting with low levels of residual moisture.
The present invention is directed to polymer blends for use in nonwoven fabric applications, fabrics formed from the polymer blends, and to methods for forming such fabrics. In one or more embodiments, the polymer blends comprise from about 70 to about 99.9 wt %, based on the total weight of the composition, of a first propylene-based polymer and from about 0.1 to about 30 wt % of a second propylene-based polymer. The first polymer has a melt flow rate of from about 100 to about 5,000 g/10 min, and the second polymer has a melt flow rate of about 1 to about 500 g/min. In various embodiments, the MFR of the first polymer may be higher than the MFR than the second polymer and/or the triad tacticity (e.g., crystallinity) of the second polymer may be higher than the first polymer. In one embodiment, the second polymer has a triad tacticity greater than about 0.94. Additionally, nonwoven fabrics, particularly meltblown nonwoven fabrics, formed from the polymer blends of the invention provide the advantages of a polymer produced with a metallocene catalyst while maintaining comparable loft and resistance to linting or roping to fabrics made from Ziegler-Natta based polymers. These fabrics also have low levels of residual moisture resulting from their manufacture and are suitable for use in many commercial applications, including sorbent articles. In certain applications low levels of “shot” and high liquid barrier properties are desirable. Blends of high MFR metallocene based with lower MFR or higher crystallinity propylene-based polymers reduce “shot” and/or improve barrier resistance, particularly to water based liquids.
The nonwoven fabrics of the present invention are formed from polymer blends that comprise from about 70 to about 99.9 wt %, based on the total weight of the composition, of a first propylene-based polymer and from about 0.1 to about 30 wt % of a second propylene-based polymer, where the first polymer has a melt flow rate of from about 100 to about 5,000 g/10 min, and the second polymer a melt flow rate of from about 1 to about 500 g/min and either a lower melt flow rate or a higher triad tacticity than the first polymer. In one embodiment, the second polymer has a triad tacticity greater than about 0.94. In one or more embodiments, the first polymer is produced using a catalyst system comprising a metallocene catalyst. In the same or other embodiments, the first polymer is a reactor grade polymer.
The present invention is also directed to processes for forming nonwoven fabrics comprising the polymer blends described herein. In one or more embodiments, such methods comprise the steps of forming a molten polymer composition, forming fibers comprising the polymer composition using a meltblown process, and forming a fabric from the fibers. The molten polymer composition comprises from about 70 to about 99.9 wt %, based on the total weight of the composition, of a first propylene-based polymer prepared using a catalyst system comprising a metallocene catalyst and having a melt flow rate of from about 100 to about 5,000 g/10 min, and from about 0.1 to about 30 wt % of a second propylene-based polymer having either a lower melt flow rate and/or a higher triad tacticity (i.e., crystallinity). In one embodiment, the melt flow rate of from about 1 to about 500 g/10 min and/or a triad tacticity greater than about 0.94.
As used herein, the term “copolymer” is meant to include polymers having two or more monomers, optionally with other monomers, and may refer to interpolymers, terpolymers, etc. The term “polymer” as used herein includes, but is not limited to, homopolymers, copolymers, terpolymers, etc. and alloys and blends thereof. The term “polymer” as used herein also includes impact, block, graft, random and alternating copolymers. The term “polymer” shall further include all possible geometrical configurations unless otherwise specifically stated. Such configurations may include isotactic, syndiotactic and random symmetries. The term “blend” as used herein refers to a mixture of two or more polymers.
The term “monomer” or “comonomer” as used herein can refer to the monomer used to form the polymer, i.e., the unreacted chemical compound in the form prior to polymerization, and can also refer to the monomer after it has been incorporated into the polymer, also referred to herein as a “[monomer]-derived unit”, which by virtue of the polymerization reaction typically has fewer hydrogen atoms than it does prior to the polymerization reaction. Different monomers are discussed herein, including propylene monomers, ethylene monomers, and diene monomers.
In some embodiments of the present invention, each of the first and second propylene-based polymers comprises polypropylene. “Polypropylene” as used herein includes homopolymers and copolymers of propylene or mixtures thereof. Products that include one or more propylene monomers polymerized with one or more additional monomers may be more commonly known as random copolymers (RCP) or impact copolymers (ICP). Impact copolymers are also known in the art as heterophasic copolymers. “Propylene-based,” as used herein, is meant to include any polymer comprising propylene-derived units, either alone or in combination with one or more comonomers, in which propylene-derived units are the major component (i.e., greater than 50 wt % propylene).
The polymer blends used to form the nonwoven fabrics of the present invention comprise a first propylene-based polymer. In one or more embodiments, the first propylene-based polymer is a reactor grade propylene polymer produced using a catalyst system comprising a metallocene compound. By “reactor grade” is meant a polymer that has not been chemically or mechanically treated after polymerization in an effort to alter the polymer's average molecular weight, molecular weight distribution, or viscosity. Particularly excluded from those polymers described as reactor grade are those that have been peroxide coated.
The first propylene-based polymer may be a homopolymer or a copolymer of propylene-derived units and one or more comonomers (e.g., C2 and/or C4-C16 alpha olefin-derived units). When the first polymer is a copolymer, the comonomer content may be from about 0.01 to about 25 wt %, or from about 0.1 to about 20 wt %, or from about 1 to about 15 wt %, or from about 1 to about 10 wt %, based upon the weight of the first polymer. In a preferred embodiment, the first polymer is a propylene homopolymer (i.e., polypropylene homopolymer).
In one embodiment, the first polymer is predominately crystalline, meaning it has a melting temperature greater than about 110° C., or greater than about 115° C., or greater than about 130° C. The term “crystalline” as used herein refers to those polymers having a heat of fusion greater than about 60 J/g, or greater than about 70 J/g, or greater than about 80 J/g, as determined by Differential Scanning calorimetry (DSC) at a heating rate of 10° C./minute.
Crystallization temperature (Tc), melting temperature (Tm), and heat of fusion (Hf) may be measured as follows. For example, about 6 to 10 mg of a sheet of the polymer or plasticized polymer is pressed at approximately 150° C. to 200° C., and is removed with a punch die. The sample is placed in a Differential Scanning calorimeter (Perkin Elmer 7 Series Thermal Analysis System) and heated to 200° C. and held for 10 minutes. The sample is cooled at 10° C./min to attain a final temperature of 25° C. The thermal output is recorded and the inflection point in the thermal output data, indicating a change in the heat capacity, is determined by electronically differentiating the thermal output data. The maximum in the differential thermal output data corresponds to the crystallization temperature of the sample. The sample is held at 25° C. for 10 minutes and heated at 10° C./min to 200° C. The thermal input is recorded and the inflection point in the thermal input data, indicating a change in the heat capacity, is determined by electronically differentiating the thermal input data. The maximum in the differential thermal input data corresponds to the melting temperature of the sample. The area under the melting peak of the sample, which typically occurs between about 0° C. and about 200° C., is measured in Joules and is a measure of the Hf of the polymer.
In one or more embodiments, the first propylene-based polymer has a melt flow rate, or “MFR” (2.16 kg, 230° C.), of from about 100 to about 5,000 g/10 min, as determined by ASTM D-1238. In further embodiments, the first polymer may have an MFR of from about 350 to about 4,000 g/10 min, or from about 500 to about 3,000 g/10 min, or from about 750 to about 2,500 g/10 min, or from about 1,000 to about 2,000 g/10 min.
In various embodiments, the first propylene-based polymer has a triad tacticity of less than about 0.96, or less than about 0.95, or less than about 0.94.
In one or more embodiments, the first propylene-based polymer may have a weight average molecular weight (Mw) of from about 40,000 to about 125,000. In the same or other embodiments, the first polymer may have a number average molecular weight (Mn) of from about 10,000 to about 60,000. The first polymer may also have a molecular weight distribution (Mw/Mn, or “MWD”) of from about 1.0 to about 4.0, or from about 1.5 to about 3.5, or from about 2.0 to about 3.0. Techniques for determining the molecular weight (Mn and Mw) and molecular weight distribution (MWD) are found in U.S. Pat. No. 4,540,753 (which is incorporated by reference herein for purposes of U.S. practice) and references cited therein and in Macromolecules, 1988, Volume 21, p. 3360 (which is herein incorporated by reference for purposes of U.S. practice) and references cited therein.
The first propylene-based polymer is produced using a catalyst system comprising a metallocene catalyst. In one or more embodiments, the catalyst system comprises at least one metallocene, preferably supported using a porous particulate material, and at least one activator. The catalyst system may also comprise one or more cocatalysts.
As used herein, “metallocene” refers generally to compounds represented by the formula CpmMRnXq, where Cp is a cyclopentadienyl ring which may be substituted, or derivative thereof which may be substituted, M is a Group 4, 5, or 6 transition metal, for example titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo) or tungsten (W), R is a hydrocarbyl group or hydrocarboxyl group having from one to 20 carbon atoms, X is a halogen or hydrogen, and m=1-3, n=0-3, q=0-3, and the sum of m+n+q is equal to the oxidation state of the transition metal.
Methods for making and using metallocenes are disclosed in, for example U.S. Pat. Nos. 4,530,914; 4,542,199; 4,769,910; 4,808,561; 4,871,705; 4,933,403; 4,937,299; 5,017,714; 5,026,798; 5,057,475; 5,120,867; 5,278,119; 5,304,614; 5,324,800; 5,350,723, 6,143,686; and 5,391,790.
The metallocene component selected for use in the catalyst system of this invention is a metallocene which, when used alone, produces isotactic, crystalline propylene polymers and, when used in combination with another metallocene, produces polymers having the attributes desired for the particular application of interest. Metallocene catalyst components suitable for preparation of the first propylene-based polymer include those described in U.S. Pat. Nos. 6,143,686, 5,145,819; 5,243,001; 5,239,022; 5,329,033; 5,296,434; 5,276,208; and 5,374,752; and EP 549 900 and 576 970.
Metallocenes are generally used in combination with some form of activator in order to create an active catalyst system. The term “activator” is defined herein to be any compound or component, or combination of compounds or components, capable of enhancing the ability of one or more metallocenes to polymerize olefins to polyolefins.
In one embodiment, ionizing activators are used to activate the metallocenes. These activators can be “non-ionic” or “ionic” (also called non-coordinating anion activators or NCA activators). The ionic activators are compounds such as tri(n-butyl)ammonium tetrakis(pentafluorophenyl)boron, which ionize the neutral metallocene compound. Such ionizing compounds may contain an active proton, or some other cation associated with but not coordinated or only loosely associated with the remaining ion of the ionizing compound. Combinations of activators may also be used, for example, alumoxane and ionizing activators in combinations, for example those described in WO 94/07928. The non-ionic activator precursors that can serve as the NCA activators are strong Lewis acids with non-hydrolyzable ligands, at least one of which is electron-withdrawing, such as those Lewis acids known to abstract an anionic fragment from dimethyl zirconocene (biscyclopentadienyl zirconium dimethyl) e.g., trisperfluorophenyl boron, trisperfluoronaphthylboron, or trisperfluorobiphenyl boron, and other highly fluorinated trisaryl boron compounds.
The term “non-coordinating anion” describes an anion which either does not coordinate to the cationic metallocene or which is only weakly coordinated to said cation, thereby remaining sufficiently labile to be displaced by a neutral Lewis base. “Compatible” noncoordinating anions are those that are not degraded to neutrality when the initially formed complex decomposes. Further, the anion will not transfer an anionic substituent or fragment to the cation so as to cause it to form a neutral four coordinate metallocene compound and a neutral by-product from the anion. Noncoordinating anions useful in accordance with this invention are those that are compatible and stabilize the metallocene cation in the sense of balancing its ionic charge in a +1 state, yet retain sufficient lability to permit displacement by an ethylenically or acetylenically unsaturated monomer during polymerization.
The catalyst systems used to produce the polymers described herein are preferably supported using a porous particulate material, such as for example, talc, inorganic oxides, inorganic chlorides and resinous materials such as polyolefins or other polymeric compounds. In particular, the catalyst system is typically the resultant composition from contacting at least the metallocene component, the activator component, and the support component.
Desirable support materials are porous inorganic oxide materials, which include those from the Periodic Table of Elements of Groups 2, 3, 4, 5, 13 or 14 metal oxides. Silica, alumina, silica-alumina, and mixtures thereof are particularly suitable. Other inorganic oxides that may be employed either alone or in combination with the silica, alumina or silica-alumina are magnesia, titania, zirconia, and the like.
A more detailed description of the metallocene compounds, as well as activators, support materials, and overall catalyst systems, suitable for use in the present invention is found in U.S. Pat. No. 7,081,299, which is incorporated by reference herein in its entirety. In some embodiments of the invention, the metallocene used to prepare the first propylene-based polymer is a silica-supported bridged 2,4 disubstituted indenyl metallocene or bridged 4-phenyl indenyl metallocene.
The supported catalyst systems described herein and in the referenced documents can be used in any suitable polymerization technique. Methods and apparatus for effecting such polymerization reactions are well known. The supported catalyst activators can be used in similar amounts and under similar conditions to known olefinic polymerization catalysts.
As used herein, the term “polymerization” includes copolymerization and terpolymerization and the terms “olefins” and “olefinic monomer” include alpha olefins, diolefins, strained cyclic olefins, styrenic monomers, acetylenically unsaturated monomers, cyclic olefins alone or in combination with other unsaturated monomers. The metallocene supported catalyst composition is useful in coordination polymerization of unsaturated monomers conventionally known to be polymerizable under coordination polymerization conditions. Monomers suitable for the polymers of the invention include propylene and C2 and/or C4-C10 alpha-olefins. Polymerization conditions also are well known and include solution polymerization, slurry polymerization, and low pressure gas phase polymerization. The supported metallocene catalyst compositions described herein are thus particularly useful in the known operating modes employing fixed-bed, moving-bed, fluid-bed, or slurry processes conducted in single, series or parallel reactors.
Polymerization techniques for olefin polymerization can include solution polymerization, slurry polymerization, or gas phase polymerization techniques. Methods and apparatus for effecting such polymerization reactions are well known and described in, for example, 12 ENCYCLOPEDIA OF POLYMER SCIENCE AND ENGINEERING 504 541 (John Wiley and Sons, 1988) and in 2 METALLOCENE-BASED POLYOLEFINS 366 378 (John Wiley and Sons, 2000).
The polymers of the invention can be prepared with the catalysts described in either batch, semi-continuous, or continuous propylene polymerization systems. Desirable polymerization systems are the continuous processes, including diluent slurry, bulk slurry (loop and stirred tank), and gas phase (stirred and fluid bed). Continuous polymerization can be carried out in a single reactor of any of the above types, in two or more reactors operating in series, or in two or more reactors operating in parallel. When two or more reactors are operating in a continuous process, the multiple reactors can be all of the same type or they may be any combination of the types.
Hydrogen gas is often used in olefin polymerization to control the final properties of the polyolefin, such as described in POLYPROPYLENE HANDBOOK 76 78 (Hanser Publishers, 1996). Using the catalyst systems herein, it is known that higher concentrations (partial pressures) of hydrogen increase the melt flow rate (MFR) of the polyolefin generated, in particular polypropylene. The MFR can thus be influenced by the hydrogen concentration, which in turn influences the optimal fiber manufacturing process temperatures. Typically, the higher the MFR of the polypropylene, the finer the fibers and more uniform the coverage can be obtained in the fabric. Also, higher MFR resins can be processed at lower temperatures. The final quality of the fabrics made from the fibers comprising the polymers described herein is thus influenced by hydrogen concentration during polymerization or the final MFR of the polymer.
Polypropylene polymers made from the above described catalyst systems and processes have improved properties. The polypropylene tends to be highly isotactic as measured by the meso run length of the polypropylene chains, while maintaining a relatively narrow molecular weight distribution. Isotactic polypropylenes are those polymers wherein the pendent hydrocarbyl groups of the polymer chain are ordered in space on the same side or plane of the polymer backbone chain. Using isotactic polypropylene as an example, the isotactic structure is typically described as having the pendent methyl groups attached to the ternary carbon atoms of successive monomeric units on the same side of a hypothetical plane through the carbon backbone chain of the polymer, as shown in below:
The degree of isotactic regularity may be measured by NMR techniques, and typical nomenclature for an isotactic pentad is “mmmm”, in which each “m” represents a “meso” dyad or successive methyl groups on the same side in the plane. Single insertions of inverted configuration give rise to rr triads as shown below:
As is known in the art, any deviation or inversion in the regularity of the polymer structure lowers the degree of isotacticity and hence crystallinity of which the polymer is capable. Ideally, the longer the mmmm runs or meso run lengths, the more highly isotactic the polypropylene. Defects and inversions such as the 1, 3 or 2, 1 insertion are undesirable when isotactic polymer is desired.
In some embodiments, the first propylene-based polymer of the present invention may have less than 50 stereo defects per 1000 units, or less than 25 stereo defects per 1000 units, or less than 100 stereo defects per 10,000 units, or less than 80 stereo defects per 10,000 units, and meso run lengths (MRL) of greater than 50, or greater than 75, or greater than 100 in yet another embodiment as indicated by 13C NMR.
Exemplary commercially available polymers suitable for use as the first propylene-based polymer include Achieve™ propylene polymers, available from ExxonMobil Chemical Company, and Metocene™ and Moplen™ propylene polymers, available from LyondellBasell.
The polymer blends used to form the nonwoven fabrics of the present invention comprise a second propylene-based polymer. The second propylene-based polymer may be a homopolymer or a copolymer of propylene with one or more C2 and/or C4-C10 alpha olefins.
The second propylene-based polymer differs primarily from the first propylene-based polymer in that it has either a lower MFR than that described above for the first polymer or a higher crystallinity. In one or more embodiments herein, the second propylene-based polymer has an MFR of from about 0.1 to about 500 g/10 min, or from about 1 to about 250 g/10 min, or from about 5 to about 150 g/10 min, or from about 10 to about 100 g/10 min, or from about 10 to about 75 g/10 min, as determined by ASTM D-1238 (2.16 kg, 230° C.).
In other embodiments herein, the second propylene-based polymer may have an MFR similar to, or even higher than, that of the first propylene-based polymer, but has a crystallinity higher than that of the first propylene-based polymer. The crystallinity is reflected in the level of isotacticity of the polymer, and in such embodiments the triad tacticity of the second polymer is greater than about 0.94, or greater than about 0.95, or greater than about 0.96. As used herein, the “triad tacticity” of a polymer is the relative tacticity of a sequence of two adjacent propylene units, a chain consisting of head to tail bonds, expressed as a binary combination of m and r sequences. It is usually expressed as the ratio of the number of units of the specified tacticity to all of the propylene triads in the copolymer. The triad tacticity (mmmm fraction) of a propylene copolymer can be determined from a 13C NMR spectrum of the propylene copolymer and the following formula:
mmFraction=PPP(mm)/(PPP(mm)+PPP(mr)+PPP(rr))
where PPP(mm), PPP(mr), and PPP(rr) denote peak areas derived from the methyl groups of the second units in the following three propylene unit chains consisting of head-to-tail bonds:
The 13C NMR spectrum of the propylene copolymer is measured as described in U.S. Pat. No. 5,504,172. The spectrum relating to the methyl carbon region (19-23 parts per million (ppm)) can be divided into a first region (21.2-21.9 ppm), a second region (20.3-21.0 ppm) and a third region (19.5-20.3 ppm). Each peak in the spectrum was assigned with reference to an article in the journal Polymer, Volume 30 (1989), p. 1350. In the first region, the methyl group of the second unit in the three propylene unit chain represented by PPP (mm) resonates. In the second region, the methyl group of the second unit in the three propylene unit chain represented by PPP (mr) resonates, and the methyl group (PPE-methyl group) of a propylene unit whose adjacent units are a propylene unit and an ethylene unit resonates (in the vicinity of 20.7 ppm). In the third region, the methyl group of the second unit in the three propylene unit chain represented by PPP (a) resonates, and the methyl group (EPE-methyl group) of a propylene unit whose adjacent units are ethylene units resonates (in the vicinity of 19.8 ppm). The calculation of the triad tacticity is outlined in the techniques shown in U.S. Pat. No. 5,504,172. Subtraction of the peak areas for the error in propylene insertions (both 2,1 and 1,3) from peak areas from the total peak areas of the second region and the third region, the peak areas based on the 3 propylene units-chains (PPP(mr) and PPP(rr)) consisting of head-to-tail bonds can be obtained. Thus, the peak areas of PPP(mm), PPP(mr) and PPP(rr) can be evaluated, and hence the triad tacticity of the propylene unit chain consisting of head-to-tail bonds can be determined.
In one or more embodiments herein, the second polymer may comprise low amounts of comonomer, such that the second polymer may be a random copolymer of polypropylene (RCP) or an impact copolymer (ICP). Exemplary RCPs typically comprise from about 1 to about 8 wt % comonomer, or from about 2 to about 5 wt % comonomer. In one or more embodiments, the RCP comonomer is ethylene.
In some embodiments of the present invention, the second polymer is a copolymer of propylene and from about 0.1 to about 25 wt % of one or more comonomers. The comonomers may be linear or branched. In one or more embodiments, linear comonomers may include ethylene and/or C4 to C10 alpha-olefins, including but not limited to butene, hexene, and octene. Branched comonomers may include 4-methyl-1-pentene, 3-methyl-1-pentene, and 3,5,5-trimethyl-1 hexene. In one or more embodiments, the comonomer can include styrene.
In some embodiments, the second polymer is a copolymer of propylene and ethylene (and may comprise other comonomers as well). For example, the second polymer may comprise from about 75 to about 99 wt % units derived from propylene and from about 1 to about 25 wt % units derived from ethylene. In some embodiments, the second polymer may comprise from about 2 to about 25 wt % ethylene-derived units, or from about 3 to about 18 wt % ethylene-derived units, or from about 5 to about 10 wt % ethylene-derived units.
Optionally, the second polymer may also include one or more dienes. The term “diene” is defined as a hydrocarbon compound that has two unsaturation sites, i.e., a compound having two double bonds connecting carbon atoms. Depending on the context, the term “diene” refers broadly to either a diene monomer prior to polymerization, e.g., forming part of the polymerization medium, or a diene monomer after polymerization has begun (also referred to as a diene monomer unit or a diene-derived unit). Exemplary dienes suitable for use in the present invention include, but are not limited to, butadiene, pentadiene, hexadiene (e.g., 1,4-hexadiene), heptadiene (e.g., 1,6-heptadiene), octadiene (e.g., 1,7-octadiene), nonadiene (e.g., 1,8-nonadiene), decadiene (e.g., 1,9-decadiene), undecadiene (e.g., 1,10-undecadiene), dodecadiene (e.g., 1,11-dodecadiene), tridecadiene (e.g., 1,12-tridecadiene), tetradecadiene (e.g., 1,13-tetradecadiene), pentadecadiene, hexadecadiene, heptadecadiene, octadecadiene, nonadecadiene, icosadiene, heneicosadiene, docosadiene, tricosadiene, tetracosadiene, pentacosadiene, hexacosadiene, heptacosadiene, octacosadiene, nonacosadiene, triacontadiene, and polybutadienes having a molecular weight (Mw) of less than 1000 g/mol. Examples of straight chain acyclic dienes include, but are not limited to 1,4-hexadiene and 1,6-octadiene. Examples of branched chain acyclic dienes include, but are not limited to 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, and 3,7-dimethyl-1,7-octadiene. Examples of single ring alicyclic dienes include, but are not limited to 1,4-cyclohexadiene, 1,5-cyclooctadiene, and 1,7-cyclododecadiene. Examples of multi-ring alicyclic fused and bridged ring dienes include, but are not limited to tetrahydroindene; norbornadiene; methyltetrahydroindene; dicyclopentadiene; bicyclo(2.2.1)hepta-2,5-diene; and alkenyl-, alkylidene-, cycloalkenyl-, and cylcoalkylidene norbornenes [including, e.g., 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene]. Examples of cycloalkenyl-substituted alkenes include, but are not limited to vinyl cyclohexene, allyl cyclohexene, vinylcyclooctene, 4-vinylcyclohexene, allyl cyclodecene, vinylcyclododecene, and tetracyclododecadiene. In some embodiments of the present invention, the diene is selected from 5-ethylidene-2-norbornene (ENB); 1,4-hexadiene; 5-methylene-2-norbornene (MNB); 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; vinyl norbornene (VNB); dicyclopentadiene (DCPD), and combinations thereof. In one or more embodiments, the diene is ENB.
When one or more dienes is present, the second polymer may comprise from 0.05 to about 6 wt % diene-derived units. In further embodiments, the second polymer comprises from about 0.1 to about 5.0 wt % diene-derived units, or from about 0.1 to about 3.0 wt % diene-derived units, or from about 0.1 to about 1.0 wt % diene-derived units.
In one or more embodiments, the second polymer may have a heat of fusion (Hf) determined according to the DSC procedure described above, which is greater than or equal to about 0.5 Joules per gram (J/g), and is less than or equal to about 80 J/g, or less than or equal to about 75 J/g, or less than or equal to about 70 J/g, or less than or equal to about 60 J/g, or less than or equal to about 50 J/g. In other embodiments herein, the second polymer may have a heat of fusion greater than about 80 J/g, or greater than about 90 J/g, or greater than 100 J/g.
The first and second polymers may have the same or different melting point. In some embodiments, the melting point of the second polymer may be less than the melting point of the first polymer, such as less than 100° C., or less than 90° C., or less than or equal to 80, or less than or equal to 75° C. In other embodiments, the second polymer has a melting point higher than that of the first polymer, such as greater than 110° C., or greater than 120° C., or greater than 130° C. In certain embodiments herein, the first and second polymers both have a melting point greater than about 110° C., and the melting point of the second polymer is at least about 5° C. greater than the melting point of the first polymer.
The second polymer may further have a triad tacticity of three propylene units, as measured by 13C NMR, of 75% or greater, 80% or greater, 82% or greater, 85% or greater, or 90% or greater. In some embodiments, the triad tacticity of the second polymer ranges from about 50 to about 99%, or from about 60 to about 99%, or from about 75 to about 99%, or from about 80 to about 99%, or from about 60 to about 97%. Triad tacticity is determined by the methods described in U.S. Patent Application Publication 2004/0236042, which is incorporated herein by reference.
In various embodiments, the second propylene-based polymer has a higher melting temperature (Tm) than the first propylene-based polymer. For example, in one embodiment, the first propylene-based polymer has a melting temperature of about 153-155° C. and the second polymer has a Tm≧156° C. The second propylene-based polymer may be prepared using a metallocene catalyst system like those described above with respect to the first polymer. Alternately, the second polymer may be prepared using any other catalyst known in the art to produce polymers having the characteristics described herein, such as other single-site catalysts, Ziegler-Natta catalysts, and the like. In certain embodiments herein, the second polymer is produced using a Ziegler-Natta catalyst.
Exemplary commercially available polymers suitable for use as the second propylene-based polymer include Achieve™ and ExxonMobil™ propylene polymers (such as but not limited to PP3155E1, PP3155E3, PP3885, PP3864F5, PP3325E1, PP3374E3, and Achieve™ 3854), and Vistamaxx™ elastomers, available from ExxonMobil Chemical Company, Versify™ polymers available from the Dow Chemical Company, and Moplen HP561R, Moplen HP566R, Moplen HP462R available from Lyondell Basell, PPH9099 and PPH9020 available from Totalfina, HG455FB available from Borealis, HG3600 available from Arco, DR7052.01 available from Dow, 201-CA25 available from Ineos, and PP512P available from Sabic.
The nonwoven fabrics of the present invention are formed from a blend of the first and second propylene-based polymers described herein. In certain embodiments of the present invention, the fabrics may comprise from about 70 wt % to about 99.9 wt %, or from about 75 wt % to about 99 wt %, or from about 80 wt % to about 98 wt %, or from about 85 wt % to about 95 wt % of the first polymer and from about 0.1 wt % to about 30 wt %, or from about 1 wt % to about 25 wt %, or from about 2 wt % to about 20 wt %, or from about 5 wt % to about 15 wt % of the second polymer.
In one embodiment, the polymer composition used to form the nonwoven fabric consists essentially of the first propylene-based polymer and the second propylene-based polymer. As used herein, “consists essentially of the first propylene-based polymer and the second propylene-based polymer” means the nonwoven fabric comprises less than 2 wt % of other components, based on total weight of the polymer composition.
The present invention is directed not only to nonwoven fabrics, but also to processes for forming nonwoven fabrics comprising the polymer blends described herein. In one or more embodiments, such methods comprise the steps of forming a molten polymer composition comprising the first propylene-based polymer and the second propylene-based polymer, forming fibers comprising the polymer composition, and forming a fabric from the fibers.
The first and second polymers may be blended by any post reactor method that guarantees an intimate mixture of the components. Blending and homogenation of polymers are well known in the art and include single and twin screw mixing extruders, static mixers for mixing molten polymer streams of low viscosity, impingement mixers, as well as other machines and processes designed to disperse the first and second polymers in intimate contact. For example, the polymer components and other minor components can be blended by melt blending or dry blending in continuous or batch processes. These processes are well known in the art and include single and twin screw compounding extruders, as well as other machines and processes designed to melt and homogenize the polymer components intimately. The melt blending or compounding extruders usually are equipped with a pelletizing die to convert the homogenized polymer into pellet form. The homogenized pellets can then be fed to the extruder of fiber or nonwoven process equipment to produce fiber or fabrics. Alternately, the first and second polymers may be dry blended and fed to the extruder of the nonwoven process equipment.
The blend of the first and second polymers may also be produced by any reactor blend method currently known in the art. A reactor blend is a highly dispersed and mechanically inseparable blend of the polymers produced in situ as the result of sequential polymerization of one or more monomers with the formation of one polymer in the presence of another. The polymers may be produced in any of the polymerization methods described above. The reactor blends may be produced in a single reactor or in two or more reactors arranged in series. The blend of the first and second polymers may further be produced by combining reactor blending with post reactor blending.
The blended polymer resin may be used to produce nonwoven fabric products. As used herein, “nonwoven” refers to a textile material that has been produced by methods other than weaving. In nonwoven fabrics, the fibers are processed directly into a planar sheet-like fabric structure by passing the intermediate one-dimensional yarn state, and then are either bonded chemically, thermally, or interlocked mechanically (or both) to achieve a cohesive fabric.
The nonwoven fabrics of the present invention can be formed by any method known in the art. Preferably, the nonwoven fabrics are produced by a meltblown or spunbond process.
In a typical spunbond process, polymer is supplied to a heated extruder to melt and homogenize the polymers. The extruder supplies melted polymer to a spinnerette where the polymer is fiberized as passed through fine openings arranged in one or more rows in the spinnerette, forming a curtain of filaments. The filaments are usually quenched with air at a low temperature, drawn, usually pneumatically, and deposited on a moving mat, belt or “forming wire” to form the nonwoven fabric. See, for example, in U.S. Pat. Nos. 4,340,563; 3,692,618; 3,802,817; 3,338,992, 3,341,394; 3,502,763; and U.S. Pat. No. 3,542,615.
The fibers produced in the spunbond process are usually in the range of from about 10 to about 50 microns in diameter, depending on process conditions and the desired end use for the fabrics to be produced from such fibers. For example, increasing the polymer molecular weight or decreasing the processing temperature results in larger diameter fibers. Changes in the quench air temperature and pneumatic draw pressure also have an affect on fiber diameter.
As used herein, “meltblown fibers” and “meltblown fabrics” refer to fibers formed by extruding a molten thermoplastic material at a certain processing temperature through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web or nonwoven fabric of randomly dispersed meltblown fibers. Such a process is generally described in, for example, U.S. Pat. Nos. 3,849,241 and 6,268,203. Meltblown fibers are microfibers that are either continuous or discontinuous and are generally smaller than about 10 microns, preferably less than about 5 microns. The term meltblowing as used herein is meant to encompass the meltspray process.
Commercial meltblown processes utilize extruders having a relatively high throughput, in excess of 0.3 grams per hole per minute (“ghm”), or in excess of 0.4 ghm, or in excess of 0.5 ghm, or in excess of 0.6 ghm, or in excess of 0.7 ghm. The fabrics of the present invention may be produced using commercial meltblown processes, or in test or pilot scale processes. In one or more embodiments of the present invention, the fibers used to form the nonwoven fabrics are formed using an extruder having a throughput rate of from about 0.1 to about 3.0 ghm, or from about 0.2 to about 2.0 ghm, or from about 0.3 to about 1.0 ghm.
The fabrics described herein may be a single layer, or may be multilayer laminates. One application is to make a laminate (or “composite”) from meltblown fabric (“M”) and spunbond fabric (“S”), which combines the advantages of strength from spunbonded fabric and greater barrier properties of the meltblown fabric. A typical laminate or composite has three or more layers, a meltblown layer(s) sandwiched between two or more spunbonded layers, or “SMS” fabric composites. Examples of other combinations are SSMMSS, SMMS, and SMMSS composites. Composites can also be made of the meltblown fabrics of the invention with other materials, either synthetic or natural, to produce useful articles.
One parameter often used to describe nonwoven fabrics is their basis weight, or the weight of the fabric per unit of area. The fabrics of the present invention may have a basis weight of from about 0.1 to about 500 grams per square meter (“gsm”), or from about 1 to about 450 gsm, or from about 10 to about 400 gsm, or from about 25 to about 350 gsm.
A variety of additives may be incorporated into the polymers used to make the fibers and fabrics described herein, depending upon the intended purpose. Such additives may include, but are not limited to, stabilizers, antioxidants, fillers, colorants, nucleating agents, dispersing agents, mold release agents, slip agents, fire retardants, plasticizers, pigments, vulcanizing or curative agents, vulcanizing or curative accelerators, cure retarders, processing aids, tackifying resins, and the like. Other additives may include fillers and/or reinforcing materials, such as carbon black, clay, talc, calcium carbonate, mica, silica, silicate, combinations thereof, and the like. Primary and secondary antioxidants include, for example, hindered phenols, hindered amines, and phosphates. Nucleating agents include, for example, sodium benzoate and talc. Also, to improve crystallization rates, other nucleating agents may also be employed such as Ziegler-Natta olefin products or other highly crystalline polymers. Other additives such as dispersing agents, for example, Acrowax C, can also be included. Slip agents include, for example, oleamide and erucamide. Catalyst deactivators are also commonly used, for example, calcium stearate, hydrotalcite, and calcium oxide, and/or other acid neutralizers known in the art.
The nonwoven products described above may be used in many articles such as hygiene products including, but not limited to, diapers, feminine care products, and adult incontinent products. The nonwoven products may also be used in medical products such as sterile wrap, isolation gowns, operating room gowns, surgical gowns, surgical drapes, first aid dressings, and other disposable items.
The fabrics of the present invention are also useful as air or liquid filters. Examples of filter applications include automotive and vehicle cabin filters, home ventilation filters, clean room filters, industrial ash and particulates filters, surgical and nuisance dust masks, beverage filters, pharmaceutical filters, medical filters, water purification filters, and recreational filters such as pool filters. The filters may be useful in either sheet or cartridge form, and may be multi-layered or multi-density.
The fabrics of the present invention are also useful as sorbent products, such as oil sorbent, chemical sorbent, or water sorbent articles. Some other specific nonwoven articles include, but are not limited to, swimwear, outerwear, scrubbing pads, cloth linings, automotive interior parts, face masks and respirators, vacuum bags, wipe materials, and other products.
In the examples below, a first propylene-based polymer, labeled “Component A”, and a second propylene-based polymer, labeled “Component B”, were used either individually or blended to form a polymer resin that was meltblown to form nonwoven fabrics. The fabrics were formed on a BIAX pilot line, commercially available from BIAX-Fiberfilm in Greenville, Wis. The pilot line was equipped with a 3.5″ extruder capable of a throughput of approximately 300+ lb/hr and a 25″ (0.635 m) wide capillary die having approximately 200 holes/inch (0.015″ capillary size). The maximum throughput rate of the extruder was approximately 0.57 ghm. The line was also equipped with a 1 m diameter single drum collector. The ambient temperature at the time of testing was approximately 60° F. (15.5° C.). All fabric examples reported below had a basis weight of approximately 300 gsm.
Component A is a metallocene-catalyzed reactor grade propylene homopolymer having an MFR of about 1550 g/10 min.
Component B1 is a Ziegler-Natta catalyzed propylene homopolymer having an MFR of about 36 g/10 min.
Component B2 is a Ziegler-Natta catalyzed propylene homopolymer having an MFR of about 65 g/10 min.
Component B3 is a metallocene-catalyzed propylene-based elastomer having an ethylene comonomer content of 13 wt % and an MFR of about 290 g/10 min.
Component B4 is a peroxide coated Zeigler-Natta catalyzed propylene homopolymer having an MFR of about 1200 g/10 min.
As used herein, one inch is equivalent to 2.54 centimeters. Degrees Fahrenheit (° F.) can be converted to degrees Celsius (° C.) as follows: ° C.=(° F.−32)×5/9.
In Comparative Example 1, fabrics were prepared using 100 wt % Component A at varying throughput rates, air temperatures, die pressures, and water quench rates. The resulting fabrics were observed visually and tactilely, and the results are reported in Table 1.
In Example 2, fabrics were prepared using 95 wt % Component A and 5 wt % Component B1 at varying throughput rates, air temperatures, die pressures, and water quench rates. The resulting fabrics were observed visually and tactilely, and the results are reported in Table 2.
In Example 3, fabrics were prepared using 90 wt % Component A and 10 wt % Component B1 at varying throughput rates, air temperatures, die pressures, and water quench rates. The resulting fabrics were observed visually and tactilely, and the results are reported in Table 3.
In Example 4, fabrics were prepared using 90 wt % Component A and 10 wt % Component B2 at varying throughput rates, air temperatures, die pressures, and water quench rates. The resulting fabrics were observed visually and tactilely, and the results are reported in Table 4.
In Example 5, fabrics were prepared using 90 wt % Component A and 10 wt % Component B3 at varying throughput rates, air temperatures, die pressures, and water quench rates. The resulting fabrics were observed visually and tactilely, and the results are reported in Table 5.
In Comparative Example 6, fabrics were prepared using 100 wt % Component B4 at varying throughput rates, air temperatures, die pressures, and water quench rates. The resulting fabrics were observed visually and tactilely, and the results are reported in Table 6.
As reflected in the Examples and Tables above, the addition of a small amount of a lower MFR polymer or a polymer with a triad tacticity greater than about 0.94 or 0.95 or 0.96 (Component B) to a high MFR metallocene-catalyzed reactor grade homopolypropylene (Component A) helps to improve loft and reduce ropiness (i.e., poor filament separation) in meltblown nonwoven fabrics made from the polymer blend. The addition of a second polymer is believed to improve the solidification rate of the first polymer by either increasing the elongation viscosity which allows higher process temperatures and therefore higher water quench rates for faster cooling without leaving high residual moisture or by increasing the crystallization rate by nucleating the metallocene polymer. Faster solidification or crystallization tends to produce more loft in the fabric.
Table 7 (Blends of metallocene-catalyzed polypropylene meltblown with Ziegler-Natta meltblown). Blend 1=10 wt % of Component A (a Ziegler-Natta-catalyzed polypropylene having a MFR of 400 gr/min) and 90 wt % of Component B (a metallocene-catalyzed polypropylene having a MFR of 1400 gr/min) and Blend 2=20 wt % of Component A and 80 wt % of Component B, the wt % based upon total weight of the blend:
Table 7 (series 2.9-2.18) shows the process conditions and properties of a melt blown fabric made with a metallocene catalyzed polymer (˜1400MFR). Blending a lower MFR polymer made with a Z—N catalyst (Blend 1 with a 400 MFR reactor grade) allows the production of fabrics with lower levels of shot at moderately high throughput rates (0.6 ghm) even at fairly low process temperatures (480° F.). At high throughput rates (0.75 ghm) and/or high process temperatures (510° F.), Blend 2 allows the production of fabrics with greatly reduced shot levels and improved barrier properties (higher hydrohead or “HH”).
The present invention can be further described as follows:
1. A nonwoven fabric made from a polymer composition comprising:
a. from about 70 to about 99.9 wt %, based on the total weight of the composition, of a first propylene-based polymer having a melt flow rate of from about 100 to about 5,000 g/10 min; and
b. from about 0.1 to about 30 wt % of a second propylene-based polymer having a melt flow rate of from about 1 to about 500 g/10 min, wherein the second propylene-based polymer has at least one of: (i) a lower melt flow rate than the first propylene-based polymer; or (ii) a higher crystallinity than the first propylene-based polymer;
wherein the first propylene-based polymer is prepared using a catalyst system comprising a metallocene catalyst.
2. The fabric of 1, wherein the polymer composition comprises from about 5 to about 15% by weight of the second propylene-based polymer.
3. The fabric of 1, wherein the second propylene-based polymer is prepared using a catalyst system comprising a Ziegler-Natta catalyst.
4. The fabric of 1, wherein the fabric is meltblown.
5. The fabric of 1, wherein the first propylene-based polymer is a propylene homopolymer.
6. The fabric of 5, wherein the first propylene-based polymer is a reactor grade propylene homopolymer.
7. The fabric of 1, wherein the second propylene-based polymer is a propylene homopolymer.
8. The fabric of 1, wherein the second propylene-based polymer further comprises from 0.01 to 25% by weight of the second polymer of one or more comonomers selected from C2 and/or C4-C10 alpha-olefins.
9. The fabric of 1, wherein the first propylene-based polymer has a melt flow rate of from about 500 to about 3000 g/10 min.
10. The fabric of 1, wherein the second propylene-based polymer has a melt flow rate of from about 1 to about 250 g/10 min.
11. The fabric of 1, wherein the second propylene-based polymer has a melt flow rate of from about 1 to about 50 g/10 min.
12. The fabric of 1, wherein the first polymer has a triad tacticity of greater than about 0.94.
13. The fabric of 1, wherein the second propylene-based polymer has a higher triad tacticity than the first propylene-based polymer.
14. The fabric of 1, wherein the first propylene-based polymer has a meso run length, as determined by 13C NMR, greater than about 75.
15. An article comprising the fabric of 1.
16. The article of 15, wherein the article is selected from one or more of a hygiene product, a medical product, a filter medium, an oil sorbent product, a water sorbent product, or a chemical sorbent product.
17. A process for producing nonwoven fabrics comprising:
a. forming a molten polymer composition comprising: (i) from about 70 to about 99.9 wt %, based on the total weight of the composition, of a first propylene-based polymer prepared using a catalyst system comprising a metallocene catalyst and having a melt flow rate of from about 100 to about 5,000 g/10 min; and (ii) from about 0.1 to about 30 wt % of a second propylene-based polymer having a melt flow rate of from about 1 to about 500 g/10 min wherein the second propylene-based polymer has at least one of: (i) a lower melt flow rate than the first propylene-based polymer; or (ii) a higher crystallinity than the first propylene-based polymer;
b. forming fibers comprising the polymer composition using a meltblown process; and
c. forming a fabric from the fibers.
18. The process of 17, wherein the second propylene-based polymer has a higher triad tacticity than the first propylene-based polymer.
19. The process of 17, wherein the second propylene-based polymer is prepared using a catalyst system comprising a Ziegler-Natta catalyst.
20. The process of 17, wherein the first propylene-based polymer is a propylene homopolymer.
21. The process of 20, wherein the first propylene-based polymer is a reactor grade propylene homopolymer.
22. The process of 17, wherein the second propylene-based polymer is a propylene homopolymer.
23. The process of 17, wherein the second propylene-based polymer further comprises from 0.01 to 25% by weight of the second polymer of one or more comonomers selected from C2 and/or C4-C10 alpha-olefins.
24. The process of 17, wherein the first propylene-based polymer has a melt flow rate of from about 500 to about 3000 g/10 min.
25. The process of 17, wherein the first propylene-based polymer has an MWD of from about 1.0 to about 4.0.
26. The process of 17, wherein the first propylene-based polymer has a meso run length, as determined by 13C NMR, greater than about 75.
27. The process of 17, wherein the fibers are formed using an extruder having a throughput rate of from about 0.1 to about 3 ghm.
28. The process of 27, wherein the throughput rate is from about 0.3 to about 1.0 ghm.
29. The process of 27, wherein the melt temperature of the extruder is from about 175° C. to about 290° C.
30. The process of 17, wherein the air temperature of the meltblown process is from about 175° C. to about 290° C.
31. The process of 17, wherein the air pressure at the die of the meltblown process is about 10 kPa to about 215 kPa.
32. The process of 17, wherein the fabric has a basis weight of from about 0.1 to about 500 g/m2.
Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. All numerical values are “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.
Various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Furthermore, all patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims priority to U.S. Provisional Application Ser. No. 61/354,882 filed Jun. 15, 2010, the disclosure of which is fully incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2011/034967 | 5/3/2011 | WO | 00 | 1/18/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61354882 | Jun 2010 | US |
