KR20070016109A - Fibers and nonwovens comprising polypropylene blends and mixtures - Google Patents

Abstract

Nonwoven materials and fibers are disclosed that include a polymer blend and a polymer mixture incorporating a blend of a first metallocene polypropylene and a second polypropylene. The first and second polypropylenes have a predetermined relationship in the melt temperature and the melt flow rate of the individual polypropylenes. Also disclosed are nonwoven materials and fibers (including bicomponent fibers) made from fibers (including bicomponent fibers) extruded using the present polymer blends and / or polymer mixtures.

Description

FIBERS AND NONWOVENS COMPRISING POLYPROPYLENE BLENDS AND MIXTURES

A polymer blend and a polymer mixture are provided that include a mixture of first polypropylene and second polypropylene. Also provided are nonwoven materials and fibers comprising fibers comprising this polymer blend and / or polymer mixture.

Polyolefin resins such as polypropylene for use in nonwovens are difficult to manufacture and present additional challenges compared to polyolefin resins suitable for films. This is because the material and processing requirements in the manufacture of the fibers are much more stringent than in the manufacture of the films. In the manufacture of fibers, the residence time effective for forming a structure is typically much shorter and flow properties are further required for the physical and rheological properties of the material. In addition, local strain and shear / elongation are much greater in fiber manufacturing than in other processes, and small defects in the melt, slight inconsistencies, or phases in the spinning of very fine fibers. Incompatibility is not acceptable in commercially viable processes.

In general, smaller fiber diameters will enable softer nonwovens. Softer nonwovens are preferred because they are gentler to the skin, feel pleasing to the touch, and help to provide aesthetic properties more similar to garments in diapers, wipes, and other similar products.

In addition to softness, another desirable attribute sought in fibers including nonwovens is wear resistance. Wear resistance is also important because it ensures that the fibers and nonwovens have sufficient mechanical integrity during use to ensure that both the fiber and the nonwoven do not break to create undesirable fluff or lose aesthetic properties.

There is also a need for nonwovens that can have high extensibility at relatively small forces. These can be used to maintain fit in products such as diapers and to facilitate the use of various mechanical post-treatments. Typically, smaller fiber diameters and easier fiber stretching have been found to be difficult to achieve. This is because if the fiber diameter is reduced, it is usually done by increasing the spin rate or draw ratio during spinning, which reduces the stretchability of the fiber in mechanical post-treatment due to increased polymer orientation. to be.

In addition, more recently there is an increasing need in the industry for nonwovens that can also exhibit significant stretch or cold-drawability when used in disposable products. Indeed, in absorbent articles such as diapers and catamenials, the solid state activation process has become an integral part of the fabrication of many chassis components. Such a process may include improvement in softness or feel that increases the comfort and feel of the nonwoven fabric; It can provide important functional effects of loft, texture or aperturing to enhance the visual appearance, alter the transport properties, or preferably modify the mechanical properties. However, in such a process the nonwoven needs to remain intact after expanding to high strain rate.

One method in the art used to address this issue is to blend several polymer resins. For example, US Pat. No. 6,476,135 discloses polymerized high melt flow rate (MFR) propylene homopolymers (250 to 550 g / 10 min) and propylene and ethylene, suitable for the production of stretchable fibers. Or blends of random copolymers of C ₄ -C ₁₀ α-olefins are disclosed. Nonwoven fabrics formed from fibers made using propylene impact copolymer compositions are disclosed in published International Patent Publications WO 01/64979 A1 and WO 01/64979 A1. U.S. Patent 5,804,286 discloses fibers comprising various polymers, such as isotactic polypropylene, polyethylene, and block or grafted polyolefin copolymers or terpolymers that are at least partially miscible with polypropylene and polyethylene. , Nonwovens and multilayer fabrics are disclosed. Multilayer structures are also claimed in US Pat. No. 6,506,698 and WO 00/28122. U. S. Patent No. 5,616, 412 discloses a fine denier having a high elongation at break, including a blend of polypropylene and polystyrene made by forming an intimate blend using a twin screw extruder and then spinning the blend. Filaments are disclosed. Published International Patent Publication WO 01/73174 A1 discloses a process for producing a fabric comprising a plurality of fibers comprising at least one polypropylene polymer and at least one ethylene polymer.

Another method in the art to address this issue is through bicomponent fibers. For example, published international patent application WO 01/30563 discloses an elastic laminate in which a nonwoven layer comprising bicomponent fibers having a sheath-core structure is used. This sheath comprises an ethylene-propylene random copolymer comprising from about 7 mol% to about 15 mol% ethylene comonomer randomly distributed in the polymer backbone. US Pat. No. 6,417,122 discloses multicomponent fibers comprising two or more polymer components arranged in structured domains, each component comprising a multi-polymer blend of two or more different polyolefins, which are more melted. The phase is either a dominant continuous phase or a non-continuous phase.

The use of random copolymers or stereoisomers of polypropylene in fibers has also been disclosed. For example, spunbonded fabrics made of fibers having a high ethylene content (greater than 10% by weight) polypropylene copolymer and having a diameter of about 5 to about 40 microns in at least one of the components are described in US Pat. No. 6,235,664. Is disclosed. U. S. Patent No. 6,080, 818 discloses fibers, yarns or yarns comprising polymer blends of predominantly flexible atactic polyolefins with isotactic polypropylene, methods for making such fibers, yarns and yarns and Nonwoven products are disclosed.

As indicated above, there is an unmet need for extremely stretchable nonwovens that include fibers that can be made from commercially available thermoplastics without requiring expensive specialty polymers or complex manufacturing processes. It is well known that as the spinning speed increases, the molecular orientation increases, the stress for further straining the fiber increases, and the fiber drawing force decreases. This is ideal for the production of small denier fibers with high strength and low strain. However, the production of fine fibers with high extensibility at a reasonable cost remains a very serious challenge.

There is also a need for polypropylene materials suitable for use in nonwoven fibers that are easily extensible (especially at high strains) and have improved wear resistance.

Summary of the Invention

The first aspect of the invention is at least

(a) a first polypropylene having an average melt temperature T _M1 and a melt flow rate MFR ₁ ; And

(b) a second polypropylene having an average melt temperature T _M2 and a melt flow rate MFR ₂

It includes;

The average melt temperature T _Mb is from about 125 ° C. to about 160 ° C. and the melt flow rate MFR _pa is from about 10 g / 10 minutes to about 40 g / 10 minutes,

T _M1 <T _Mb <T _M2 ,

MFR ₁ <MFR _b A polymer blend is provided wherein <MFR ₂ .

Also preferably there is a minimum difference of about 10 ° C. between T _M1 and T _M2 and the minimum ratio of MFR ₂ : MFR ₁ is at least about 2.0: 1.0.

In a preferred embodiment of the invention, the first polypropylene is a metallocene resin having an average melt temperature T _M1 of about 110 ° C. to about 135 ° C. and a melt flow rate MFR ₁ of about 5 to about 25, and a second polypropylene Silver has an average melt temperature T _M2 of about 135 ° C. to about 165 ° C. and a melt flow rate MFR ₂ of about 25 g / 10 minutes to about 50 g / 10 minutes.

In an alternative embodiment of the invention, the polymer blend may comprise one or more additional polypropylenes and the polymer blend may be blended with an adjuvant.

In a further embodiment of the invention, the polymer blend or blend / adjuvant blend may be extruded into fibers suitable for use in nonwoven materials. This fiber may be present in bicomponent form comprising the polymer composition described above or further comprising additional resin.

All documents cited are hereby incorporated by reference in their associated parts and no citation of any document should be construed as an admission to the prior art for the present invention. Unless otherwise specified, all percentages, ratios, and ratios are by weight and all temperatures are in degrees Celsius (° C.). All measurements are in SI unless otherwise specified.

1 is a graph showing the relationship between the polymer blends and mixtures of the present invention and polymer blends of the prior art, together with the properties of the resins used for the preparation of the blends.

FIG. 2 is a time-related graph at 50% increase in wall shear stress and turbidity measured according to the Rheo-Optical Characterization method described herein.

Justice

As used herein, the term “polymer blend” includes but is not limited to homopolymers, copolymers (eg, block copolymers, graft copolymers, random copolymers and alternating copolymers), terpolymers, and the like. It is meant a mixture of polymers, but not limited to, and blends and variants thereof in the form of a solid solution that is a homogeneous mixture. Optional adjuvants may be added to the polymer blend, and if the blend remains a solid solution, such a blend is also considered a polymer blend.

As used herein, the term "polymer mixture" refers to a mixture of the adjuvant and polymer blends disclosed herein, wherein at least one of the adjuvant components is immiscible in the polymer blend, ie the mixture is heterogeneous Do. For example, the adjuvant is insoluble in one or both of the first polypropylene and the second polypropylene.

As used herein, the term "random copolymer" or "RCP" refers to an alpha-olefin (butene, hexene) or ethylene that is higher than propylene as a comonomer introduced into the chain in a statistical or random manner. It refers to this mixed polypropylene based copolymer. As a result, the overall crystallinity of the material is reduced due to the lower self-similarity of the polymer chain which negatively affects the ability of the material to crystallize. If no comonomer is incorporated into the chain at all, a polypropylene homopolymer is obtained.

As used herein, the term “spunbonded fiber” refers to a small diameter, substantially continuous fiber formed by extruding molten thermoplastic material into filaments from a plurality of fine, usually circular capillaries of spinnerets. The diameter of the extruded filaments is then rapidly reduced by using conventional godet winding systems or by drawing through an air drag damping device. If a Godet system is used, the fiber diameter can be further reduced through drawing after extrusion.

As used herein, the term " extensible " refers to a failure capable of stretching at least about 200%, preferably causing catastrophic, without experiencing a failure that would cause catastrophic upon application of a biasing force. Stretched to 400% or more without experience, more preferably stretched to 600% or more without experiencing a failure that would cause catastrophe, most preferably stretched to 800% or more without experiencing a failure that would cause catastrophe Refers to any fiber. Elongation at break can be measured as described in the Test Methods section below and is defined as the breakage extension length minus the initial test gage length divided by the initial test gage length and multiplied by 100 .

As used herein, the “equivalent diameter” of a fiber of non-circular cross section is the diameter of a circle whose cross sectional area is the same as the fiber.

As used herein, the term "nonwoven web" or "nonwoven material" refers to a web having a structure of individual fibers or yarns that are sandwiched in a regular or non-repetitive manner. Nonwoven webs have been formed in a variety of processes in the past, including, but not limited to, air laying processes, meltblowing processes, spunbonding processes, and carding processes.

As used herein, the terms "consolidation" and "consolidated" combine at least a portion of the fibers of the nonwoven web to bring them closer together so that external forces, such as abrasion forces, as compared to unconsolidated webs, are combined. And forming site (s) that function to increase the resistance of the nonwoven to tensile force. "Condensed" can refer to an entire nonwoven web that has been processed such that at least a portion of the fibers are closer together, such as by thermal point bonding. Such a web may be considered a "consolidated web." In other senses, certain discrete fiber regions that are in close proximity, such as individual thermal bond sites, may be described as "consolidated."

As used herein, the term " absorbent article " refers to a device that absorbs and retains body exudates, and more specifically, absorbs various exudates that are discharged from the body located at or close to the wearer's body. We say apparatus to have.

The term "disposable" is used herein to describe absorbent articles which are not intended to be washed or otherwise restored or reused as absorbent articles (ie, they are preferably recycled or composted so that they are disposed of after one use). composted) or intended to be handled in an environmentally friendly way).

Polymer blends

The polymer blend of the present invention comprises at least a first polypropylene and a second polypropylene. Without being bound by theory, it is believed that the best features of the polyethylene component are combined in the polymer blend of the present invention. In particular, 1) low melt temperature, low melt flow rate components provide strength to the fiber comprising the polymer blend (eg, breaking tensile strength) by feeding the blend a high molecular weight "backbone". Produce wear resistance and improved stability in nonwoven webs, and 2) high melt temperature, high melt flow rate components interfere with flow induced crystallization caused by expansion of low melt flow rate components of the blend, It is believed to provide improved extrusion line throughput, fiber drop and cold extensibility as compared to prior art fibers having comparable breaking point tensile strength. In the prior art, it was not recognized that such a desirable combination of properties could be achieved by specifying the constituent resin in the blend as to both melt temperature and melt flow rate and how these properties are related. The multidimensional (melting temperature and melt flow rate) evaluation of the resins described herein has been found to provide improved blends in which the above properties are significantly improved.

Particularly preferred blends include blends of metallocene catalyzed propylene homopolymers and metallocene catalyzed random copolymers. As will be explained in greater detail below, such blends provide both improved processing and tensile properties. It should be appreciated that all blends, including blends of polymers that meet the melt temperature and melt flow rate criteria described herein, are within the scope of the present invention. For example, as can be seen in the examples, blends of polypropylene homopolymers with metallocene catalyzed RCPs provide a significant processing effect (eg, lower melting temperatures) and at the same time at least single component poly It provides mechanical properties as good as fibers spun from propylene resins.

Without being bound by theory, the flow induced crystallization in the polymer blend is reduced by the metallocene catalyzed polymer of narrower molecular weight distribution. In other words, the range of molecular weight and composition in resins produced using non-metallocene (eg, Ziegler-Natta) technology is broader than when metallocene technology is used. Will be. High molecular weight fractions will cause premature flow induced crystallization during extrusion if the melt flow rate of some fractions of the resin is low enough to change the relationship between the first and second (polypropylene) portions of the blend. It may be. That is, instead of a blend comprising a first polypropylene having a lower melt temperature and a lower melt flow rate than the second polypropylene, a portion of the blend is less than the melt flow rate of the second polypropylene and possibly the second polypropylene. Combinations having a first polypropylene having a melt flow rate without difference. This “reverse” relationship between the first polypropylene and the second polypropylene is thought to facilitate flow induced crystallization, since part of the small melt flow rate of the resin of a wide molecular weight distribution extends during polymer extrusion. It can be associated with a semicrystalline superstructure that is believed to be formed according to (Kornfield, J. Proceedings Short course: Flow / Process Induced Crystallization of Polymers, Materials Engineering and Sciences Division, American Institute of Chemical Engineers , 2002 Annual Meeting, Indianapolis, November 3, 2002).

As illustrated in Example 4 and FIG. 2, flow induced crystallization leads to “critical” wall shear stress σ _w , where crystal formation is rapidly increased. As will be appreciated, such crystal formation (as a result of either stretching orientation or wall shear during the drawing process) is substantially dependent on the properties of the product being processed at shear stresses greater than causing the onset of flow induced crystallization. Will affect. As a result, as can be seen clearly in FIG. 2, the composition according to the invention is much less sensitive to flow induced crystallization and has the improved properties discussed above. Suitably, the blend according to the invention is approximately at σ _w of 0.11 MPa when the turbidity half time value (t _1/2 ) is measured according to the rheological optical method described in the test method section below. Greater than 1000 seconds Preferably t _1/2 is greater than about 2000 seconds and more preferably greater than 3000 seconds. In other words, the resin blends of the present invention preferably maintain low crystallization levels at elevated wall shear stress. One method of investigating such low crystallization levels is the ratio of haze half-life (t ^σw _1/2 ) to haze half-life (t ⁰ _1/2 ) under quiescent conditions at a given elevated wall shear stress. A suitable measure of elevated shear stress conditions is t _1/2 (t ^0.11 _1/2 ) at sigma _w of 0.11 MPa. Suitably, the ratio of t ^0.11 _1/2 : t ⁰ _1/2 is ^greater than about 0.33, preferably greater than about 0.5, more preferably greater than about 0.75, even more preferably greater than about 0.9.

The average melting temperature T _Mb of the polymer blends of the present invention is from about 125 ° C to about 160 ° C, preferably from about 130 ° C to about 160 ° C, more preferably from about 130 ° C to about 155 ° C. The melting temperature T _Mb of the polymer blend is greater than the melting temperature T _M1 of the first polypropylene and at the same time smaller than the melting temperature T _M2 of the second polypropylene. Also preferably there is a minimum difference of about 10 ° C. between T _M1 and T _M2 , more preferably this difference is at least about 15 ° C. This melting temperature difference is believed to help ensure minimizing flow induced crystallization. Methods of measuring the average melt temperature are provided in the Test Methods section below.

In addition, the polymer blends of the present invention have a melt flow rate MFR _b . Typically, the melt flow rate MFR _b of the polymer blend is about 10 g / 10 minutes to about 40 g / 10 minutes, preferably about 15 g / 10 minutes to about 35 g / 10 minutes, more preferably about 20 g / 10 minutes to about 30 g / 10 minutes. The MFR _b of the polymer blend is larger than MFR ₁ of the first polypropylene and at the same time smaller than MFR ₂ of the second polypropylene. Also particularly preferred is a melt flow rate ratio (MFR ₂ : MFR ₁ ) of at least about 2.0: 1.0 and at least about 2.5: 1.0. Without being bound by theory, it is believed that such ratios help to ensure that only the minimum required amount of resin of the small melt flow rate required to provide the desired mechanical properties is a component of the blend. Methods of measuring melt flow rate are provided in the Test Methods section below. Alternatively, if there are not enough samples in the measurement of melt flow rate or if it is necessary to measure the melt flow rate of a fraction of the blend, alternative molecular weight methods such as gel permeation chromatography can be used and the molecular weight and melt Known correlations between flow rates can be used to determine the melt flow rate of the blend.

Those skilled in the art will appreciate that the melt flow rates of the polymer blends described herein are suitable for the method of making the desired fiber, for example extrusion or spunbonding of staple fibers.

In an optional embodiment of the present invention, the weight ratio of the first polypropylene to the second polypropylene is about 1: 4 to about 4: 1.

In another optional embodiment of the invention, the polymer blend is about 25% to about 75% by weight of the first polypropylene and polymer blend based on the weight of the polymer blend of about 25% to about 75% second Polypropylene.

The polymer blends of the present invention are suitable for conventional blending techniques, Banbury mixers (available from Farrel Corp., Ansonia, CT) or polylab twin screw extruders suitable for the production of small batches of material. Blending the desired ingredients in the desired proportions using a device comprising a laboratory extruder such as Polylab Twin Screw Extruder (available from Thermo Electron, Karlsruhe, Germany). It may also be prepared in any suitable form, including but not limited to. Commercial scale pelletized extruders may also be used to make larger amounts of blends and the like. It is even relied on intimate mixing of the pellet premix in a fiber extrusion apparatus for final mixing into the polymer blend of the present invention to produce a premix of pellets comprising pellets of the first polypropylene and pellets of the second polypropylene. It is also possible. As will be appreciated, such a dependency on the fiber extrusion apparatus requires careful design of the extruder length, temperature profile and flight geometry to ensure proper mixing of the pellets prior to fiber extrusion.

In one embodiment, the polymer blends of the present invention may be made in a multi-gas phase reactor or slurry loop reactor. For example, a multi zone circulating polymerization reactor may comprise a continuous loop of gas divided into two zones by a liquid monomer barrier held in place by a tightly packed layer of polymer particles. The first monomer or monomer blend is introduced on one side of this layer and the second monomer or monomer blend is introduced on the other side of the layer. This approach can be used to "grow up" polymer particles comprising the "onion-like" structures of the first and second polypropylenes. Such technology is being commercialized by Basell Polyolefins of Wilmington, Delaware, USA.

First polypropylene

The polymer blend of the present invention comprises a first polypropylene. The melting temperature T _M1 of the first polypropylene is less than the melting temperature T _Mb of the polymer blend and the MFR ₁ of the first polypropylene is less than the MFR _b of the polymer blend. Especially preferred are the required T _M1 and Metallocene catalyzed polypropylene with MFR ₁ .

In an optional and preferred embodiment of the invention, the average melting temperature T _M1 of the first polypropylene is preferably from about 110 ° C. to about 135 ° C., more preferably from about 115 ° C. to about 135 ° C., even more preferably Is from about 120 ° C to about 130 ° C.

The first polypropylene melt flow rate MFR ₁ of the first polypropylene may be any suitable value less than the melt flow rate of the polymer blend, provided that the MFR _b of the polymer blend is from about 10 g / 10 minutes to about 40 g / 10 minutes to be. In an optional and preferred embodiment of the invention, the first polypropylene is about 5 g / 10 minutes to about 25 g / 10 minutes, preferably about 5 g / 10 minutes to about 20 g / 10 minutes, more preferably Preferably from about 5 g / 10 minutes to about 15 g / 10 minutes.

Suitably, the first polypropylene can be prepared using any suitable polymerization method in order to have the required T _M1 and MFR ₁ . Suitable methods include Ziegler-Natta polymerization and metallocene polymerization. Preferably, the first polypropylene is a copolymer formed by polymerization of propylene and ethylene or any of C ₄ to C ₂₀ α-olefins, which polymerization is catalyzed by a metallocene catalyst. Such copolymerization destroys the crystallinity of the polymer and consequently reduces the melting point of the polymer. Preferred are catalyzed polymerizations of metallocenes (i.e., positively charged metal ions sandwiched between two negatively charged cyclopentadienyl derivative anions), where such polymerization is This is because it provides greater accuracy in terms of the composition and molecular weight (melt flow rate) of the polymer chain as well as a wider range of chemical properties. For example, unlike traditional Ziegler-Natta catalysts, well-defined grades with both narrow composition and molecular weight distribution may be produced. The effect of the narrower distribution can be seen by comparing the properties of the blends G and H in the examples. As illustrated in the examples, Blend G, in which the metallocene polymerized first polypropylene is used, has an improved strength ratio compared to the Ziegler-Natta based blends. Such accuracy provides a specific effect on the first polypropylene by minimizing redundancy with the second polypropylene in the molecular weight distribution in order to ensure the minimization of the flow induced crystallization discussed above.

Alternatively, the melting point of the first polypropylene can be reduced by increasing the level of stereo or regio errors above that found in polymer chains in typical commercial grades. In general, the lower the self-similarity of the polymer chains, the lower the melting temperature. Self-similarity can be reduced through the incorporation of comonomers randomly incorporated along the chain, as discussed above, or alternatively by introducing steric- or region-errors along the chain. Stereo-errors are characterized by different spatial localization of pendant methyl groups in the propylene monomer molecule with respect to the chain axis. Local error is generated when propylene monomer is incorporated in a head-head or tail-tail shape. US Pat. No. 6,555,643 discloses certain metallocene catalysts that can control both the amount and distribution of steric-errors incorporated into a polypropylene chain and thus match the amount of crystallinity produced and its melting temperature.

Suitable first polypropylenes are metallocene polypropylene WINTEC WFX4T (previously known as XK1159) available from Japan Polypropylene (Tokyo, Japan) and Total Petrochemicals, Houston, Texas, USA Random Ziegler-Natta copolymer polypropylene 8650 from Total Petrochemicals USA, Inc.

Second polypropylene

The polymer blend of the present invention comprises a second polypropylene. The melting temperature T _M2 of the second polypropylene is greater than the melting temperature T _Mpa of the polymer blend and the MFR ₂ of the second polypropylene is greater than the MFR _b of the polymer blend.

In an optional and preferred embodiment of the invention, the average melting temperature T _M2 of the second polypropylene is from about 135 ° C. to about 165 ° C., preferably from about 140 ° C. to about 165 ° C., more preferably from about 145 ° C. Suitable is about 155 ° C.

The melt flow rate MFR ₂ of the second polypropylene may be any suitable value greater than the melt flow rate of the polymer blend, provided that the MFR _b of the polymer blend is from about 10 g / 10 minutes to about 40 g / 10 minutes. Suitably, MFR ₂ is from about 25 g / 10 minutes to about 50 g / 10 minutes, preferably from about 25 g / 10 minutes to about 45 g / 10 minutes, more preferably from about 30 g / 10 minutes to about 45 g / 10 min.

In an optional embodiment of the present invention, the second polypropylene is a resin having a suitable melt temperature and melt flow rate. In one preferred embodiment of the invention, the second polypropylene is polypropylene in which the polymerization is catalyzed by a metallocene catalyst.

Suitable second polypropylenes are available as ACHIEVE 3825 from ExxonMobil Chemical Company (Houston, TX).

Polymer mixture

The polymer blends of the present invention may be blended with the auxiliaries described below for the formation of a polymer mixture that is also suitable for extrusion into fibers for the formation of nonwoven materials having the desirable properties described above. Such polymer mixtures can be prepared by conventional blending techniques and apparatus, such as a Banbury mixer (available from Farrell Corporation, Ansonia, Conn.) Or a polylab twin screw extruder (Carlsruhe, Germany) suitable for the production of small batches of material. Any suitable form, such as, but not limited to, blending the desired ingredients in the desired proportions using a laboratory extruder such as Thermo Electron (Karlsruhe), It can also be prepared. Commercial scale pelletized extruders may also be used to make larger amounts of blends and the like.

Supplements

The polymer blends and polymer mixtures of the present invention may optionally include an adjuvant. Suitable auxiliaries include, but are not limited to, those typically used in fiber production, nonwoven processing, polymer compositions and polymer formation. In the case of a polymer blend, a preferred adjuvant is to form a solid solution with the polymer blend and other components of the polymer mixture, such as, but not limited to, the first and second polypropylenes, wherein the solid solution is a homogeneous mixture.

In one embodiment, the adjuvant may be a nucleating agent, antiblock agents, antistatic agents, pro-heat stabilizers, lubricants, plasticizers, ultraviolet light stabilizers (available ultraviolet light stabilizers in Tarrytown, NY, USA). TINUVIN 123 available from Ciba Specialty Chemicals North America, Materials, light stabilizers, weathering stabilizers, weld strength improvers, slip agents (oleamide) Or erucamides), dyes, antioxidants (IRGANOX 1010 available from Ciba Specialty Chemicals North America), flame retardants, pro-oxidant additives, natural oils, synthetic oils, Antiblocking agents (silic acid containing chalk), fillers and combinations thereof.

In the polymer mixture, the adjuvant is included in an amount effective to achieve the result of the presence of the adjuvant in the resulting polymer mixture. For example, the amount to stabilize for UV stabilizers, the amount to lubricate for lubricants, and so on. Typically, the polymer mixture comprises about 0.1% to about 1.0% of each one or more such subcomponents.

In another aspect, the adjuvant is selected from the group of polymers other than the first polypropylene and the second polypropylene. This group of polymers includes two subgroups of polymers soluble in the polymer blend and polymers insoluble in the polymer blend.

Soluble subgroups of polymers include, but are not limited to, polypropylene homopolymers. Also suitable are polypropylenes with significant branches. When the soluble polymer comprises additional polypropylene, in order to produce a polymer blend of three or more components, the melt temperature and melt flow rate values of the additional polypropylene are determined by the melt temperature of the additional polypropylene (s) and The melt flow rate should be within the rectangle defined by the melt temperature and melt flow rate index of the first polypropylene and the second polypropylene. In this case, the first polypropylene is considered to be the polypropylene having the lowest melting temperature and melt flow rate among the polypropylenes included in the polymer blend and the second polypropylene is considered to be the polypropylene having the highest melt temperature and melt flow rate.

In one preferred embodiment, the three component blend comprises a low level of RCP polypropylene made by Ziegler-Natta polymerization. Without wishing to be bound by theory, the control of reducing the "stickiness" of the initial fibers when the nascent fibers are extruded and drawn out in order to reduce the roping during the fiber extrusion process by the inclusion of this type of resin. Amount of flow induced crystallization is provided. As is known, lowing is a drawback in the nonwoven forming process caused by uncontrolled turbulence in the damped air stream as the extruded fibers are drawn, which is a "streak" and fibers of stretched thickness in the nonwoven web. Leads to hepatic adhesions. It is believed that the fibers are reduced because the fibers comprising the Ziegler-Natta resin are less likely to stick if they are gathered because of the reduced stickiness discussed above. In order to maintain the desirable properties resulting from resin blends of Ziegler-Natta resins, resin blends of Ziegler-Natta resins should only be used at relatively low levels. Suitably, the three component blend may comprise up to about 50% RCP Ziegler-Natta resin having melt flow rate and melt temperature characteristics comparable to that of the first polypropylene. Preferably, the three component blend comprises up to about 25% Ziegler-Natta resin, more preferably up to about 10% Ziegler-Natta resin. If such a three component blend is desired, the blend should contain at least about 5% Ziegler-Natta resin.

Polymers in the group of insoluble subgroups are intended because they form microinclusions that modify their properties in the polymer blend. For example, very low density or ultra low density (ρ <0.9 g / cc) polyethylene resins, low melt temperature polypropylene (T _M <110 ° C.), syndiotactic polypropylene or EP elastomer-containing resins (eg, ADFLEX thermoplastic polyolefin elastomers from Basel Polyolefins, Wilmington, DE) Materials that are not limited to this provide increased elasticity to the polymer mixture and as a result improve the fluff resistance, bond strength and other properties related to the absorption of mechanical energy. It is believed that the dispersed rubber phase acts as a toughening agent to improve the toughness of the bonding site and thus to increase the mechanical integrity of the web. In addition, this may modify the stretch flow characteristics encountered by the polymer melt during fiber spinning and may also cause beneficial changes in the resulting fiber morphology with respect to stretchability. Suitably, such second subgroup of polymers may be incorporated into the polymer mixture of the present invention at levels of 1% to about 25%. In a preferred embodiment of the polymer mixture of the present invention, about 1% to 15% of the polymer from the insoluble subgroup is incorporated into the polymer mixture for improved elasticity.

The second subgroup of polymers may also include polymers that form microinclusion bodies without increasing the elasticity of the blend. Such polymers include, but are not limited to, polyethylene, ethylene / (alkyl) acrylate copolymers, polyesters and nylons. Without being bound by theory, it is believed that the microinclusions formed by this type of polymer interfere with the flow of segments of the polymer chains of the first polypropylene and the second polypropylene during extrusion and thereby inhibit the flow induced crystallization process. . In other words, the microencapsulation forms streamline during extrusion (e.g., straighten the molten polymer in a random walk shape that is not under any kind of stress as a result of the extrusion force). It is thought to suppress. As indicated above, the reduction of flow induced crystallization is believed to provide lower yield stress and improved cold drawability.

fiber

In addition, fibers comprising a polymer blend or polymer mixture having an average melting temperature T _Mb and MFR _b in the ranges disclosed herein and nonwoven materials comprising the fibers are described herein relative to the first polypropylene and the second polypropylene. It has surprisingly been found to have excellent performance in terms of elongation, softness and abrasion resistance compared to fibers made from other polypropylenes such as blends using resins having average melt temperatures and melt flow rates outside the ranges specified in. In addition, the polymer blends of the present invention will typically outperform other polypropylene resins and blends of comparable MFR and melting temperatures, particularly with regard to the extent of stretch and cold drawability of fibers and webs and their ease. .

Fibers comprising the present polymer blends or polymer mixtures exhibit high stretch or cold drawability, which is desirable at exceptionally low stresses, including drawing under high strain conditions (a number of commercial processes use at strains ^greater than 200 seconds ⁻¹ Done). In addition, nonwoven webs comprising such fibers exhibit a unique combination of high performance in stretch, softness and abrasion resistance. Nonwoven webs having such a desirable combination of properties can be incorporated alone or in processes used to make a variety of inexpensive high performance disposable absorbent articles, such as diapers, incontinence briefs, training pants, feminine hygiene garments, wipes, and the like. It may be advantageous to be incorporated within the laminate, and it is particularly well suited for providing major consumer benefits such as improved comfort and fit.

Specifically, the fibers of the present invention exhibit low yield stress at comparable final tensile stress as compared to fibers of the prior art. Without wishing to be bound by theory, this preferred combination of tensile properties means that during spinning, the first polypropylene (low melt temperature, low melt flow rate) is a “molecular backbone” in which a long polymer chain gives its low melt flow rate value. Provides a final tensile stress (comparable to prior art fibers) because it transfers the force through the fiber, while the second polypropylene produces a high yield stress if its low molecular weight is otherwise It is believed to be due to the low yield stress as it withstands premature flow induced crystallization. This preferred combination of low yield stress and high final tensile stress can be most conveniently represented by a ratio of properties. As shown in Table 2, the fibers spun at high spinning speeds (ie, speeds greater than 2000 m / min) and comprising the polymer blends and mixtures of the present invention yield yield stress versus final tension over fibers spun from prior art resins. The ratio of stress is lower. Suitably, this ratio is less than 0.25, more preferably this ratio is less than 0.2.

As indicated above, the lower yield stress of the fibers of the present invention will facilitate cold drawing and at the same time the final tensile stress (ie, still comparable to fibers made using prior art resins) with improved wear resistance And bond strength. In other words, the fibers comprising the polymer blends and / or polymer blends of the present invention may be stretched and permanently expanded before they reach the maximum characteristic strength of the bond site that ultimately determines the mechanical integrity of the web or cloth. For example, the ability to withstand cold draw between intersection points in a web or cloth is greater. The result is thinner cold drawn fibers in the expanded web that provide the web with an additional softening effect while maintaining mechanical integrity and good wear resistance (by preventing the failure of the fibers at the splice).

Suitably, the yield stress of the fibers comprising the polymer blend according to the invention is less than about 40 MPa, preferably less than about 35 MPa, more preferably less than about 30 MPa. In addition, the final tensile strength of the fibers comprising the polymer blend according to the invention is at least about 100 MPa, preferably greater than about 125 MPa, more preferably greater than about 140 MPa. In order to provide the desired balance of good cold drawability and mechanical strength, the fibers of the present invention are suitable for a ratio of yield stress to final tensile stress of less than about 0.20, preferably less than about 0.175, more preferably less than about 0.15.

The fibers may be of any suitable size, ie the fibers may have a diameter or equivalent diameter of about 0.5 microns to about 200 microns. Particular preference is given to the diameter or equivalent diameter of the fiber of about 10 to about 40 microns. In other words, the fibers incorporating the polymer blends of the invention are suitably about 1 to about 10 denier, preferably about 1 to about 8 denier, more preferably about 1 to about 5 denier.

In one particularly preferred embodiment, the fibers comprise bicomponent fibers for improved compaction. Bicomponent fibers are typically used as a means of inherent fiber properties and bonding performance to better separate, typically bonding performance is sheathed for bicomponent fibers. As is well known, the bicomponent fiber comprises first and second polymer components that are coextruded to provide the fiber with the desired properties from each of the first and second polymer components (as will be appreciated, Both the first and second polymer components comprise a thermoplastic polymer). For example, the bicomponent fiber may comprise a first polymer component having a softening temperature lower than the second polymer component. Such structures reduce the risk of "burn through" during thermal consolidation.

The bicomponent fiber may be of any suitable shape. Exemplary shapes include, but are not limited to, sheath-core, island-in-the sea, side-by-side, segmented pie, and combinations thereof. It is not limited. In an optional embodiment of the present invention, the shape of the bicomponent fiber is a sheath-core shape.

Spunbond structures, staple fibers, hollow fibers and shaped fibers, such as multi-lobal fibers, including the polymer blends and mixtures of the present invention can all be made. The fibers of the present invention may have different geometrical characteristics, including round, oval, star shaped, rectangular, and various other eccentric shapes.

The size of the bicomponent fiber is comparable to only including the polymer blend or mixture of the present invention. That is, the diameter or equivalent diameter of the fibers may be from about 0.5 microns to about 200 microns. Particular preference is given to the diameter or equivalent diameter of the fiber of about 10 to about 40 microns. In other words, the fibers incorporating the polymer blends of the present invention are suitably about 1 to about 10 denier, preferably about 1 to about 5 denier, more preferably about 1 to about 3 denier.

The amount of the first polymer component and the second polymer component present in the bicomponent fiber depends on a number of factors such as, but not limited to, the polymer present, the desired use of the bicomponent fiber, the desired properties of the bicomponent fiber, and the like. Will be different. In an optional embodiment, the weight ratio of the first polymer component to the second polymer component is about 1:20 to about 20: 1.

In an optional embodiment of the present invention, the second component of the bicomponent fiber exhibits a softening temperature higher than the softening temperature of the first polymer component. Suitably, this difference in softening temperature is from about 1 ° C to about 150 ° C.

Suitably, the second polymer component is a thermoplastic polymer whose extrusion temperature is compatible with the extrusion temperature of the first polymer component. Preferred thermoplastic polymers include polyolefins, in particular polyethylene, polypropylene and polyolefin blends, and polyamides, polyesters (including polyester elastomers) and polyamides. Particularly preferred second polymer components are polyolefins such as polypropylene. An exemplary polypropylene second polymer component is PROFAX PH835, available from Basel Polyolefins, Wilmington, Delaware. Also suitable as second component are blends according to the invention, the average melting temperature of which is greater than the average melting temperature of the first component in order to provide the necessary difference in softening temperature.

When the blend of the present invention is used as the second component, a suitable first component comprises polyethylene of both the homopolymer and the blend. Suitable polyethylene homopolymers are ASPUN 6811A, available from Dow Chemical, Midland, Michigan. Particularly suitable blends are disclosed in co-pending U.S. Provisional Patent Application No. 60 / 539,299 filed on January 26, 2004 in the name of Autran et al.

Nonwoven material

Typically, the fibers described above are compacted into a nonwoven material. Consolidation can be accomplished by a method of applying heat and / or pressure to the fiber web, for example by thermal spot (ie, point) bonding. Hot spot bonding can be accomplished by passing the fibrous web through a press nip formed by two rolls, as disclosed in US Pat. No. 3,855,046, wherein one of the two rolls is heated and a plurality of surfaces on its surface. It includes the elevated point of. Consolidation methods may also include, but are not limited to, ultrasonic bonding, through-air bonding, resin bonding, and hydroentanglement. High-pressure weaving typically involves treating the fiber web using a high pressure water jet to consolidate the web through mechanical fiber entanglement (friction) in the area to be consolidated. The site is formed in the fiber tangle area. The fibers can be high pressure woven as taught in US Pat. Nos. 4,021,284 and 4,024,612.

The web can be further processed (ie, converted) once consolidated. For example, webs in the form of laminates alone or with other materials can be further processed to impart scalability to them. A method of imparting scalability to materials using interlocked corrugated rolls that permanently deforms stretchable or otherwise inelastic materials that increase with increasing machine direction or width direction is described in US Pat. No. 4,116,892. US Pat. No. 4,834,741, US Pat. No. 5,143,679, US Pat. No. 5,156,793, US Pat. No. 5,167,897, US Pat. No. 5,422,172 and US Pat. No. 5,518,801. In some embodiments, the intermediate structures may be fed into corrugated rolls that engage each other at an angle associated with the machine direction of this secondary operation. Alternatively, this secondary operation may achieve increasing expansion of the intermediate structure at localized portions using pairs of interdigitated grooved plates applied to the intermediate structure under pressure. As indicated above, the nonwoven webs of the present invention are particularly suitable for these and similar processes because of particularly desirable cold extensibility.

Nonwoven materials comprising the polymer blends of the present invention are components of disposable absorbent articles (e.g., topsheets, cuff materials, core wraps, and laminated to films or substantially impermeable to aqueous liquids). Particularly useful as a backsheet when treated to this end). The nonwoven web of the present invention is a disposable diaper, disposable incontinence briefs, disposable training pants, disposable pads or sheets for floor cleaning systems, for example a sweeper manufactured by The Procter & Gamble Company. SWIFFER® may find beneficial uses as components of disposable absorbent articles, such as, but not limited to, cleaning systems, sanitary products, disposable wipes, and the like, but their use is not limited to disposable absorbent articles. . The nonwoven webs of the present invention can be used for any use that requires softness and extensibility or that benefits from softness and extensibility.

The nonwoven webs of the present invention may also be in laminate form. Laminates include, but are not limited to, thermal bonding, spray adhesives, hot melt adhesives, latex based adhesives, etc., adhesive bonding, sonic and ultrasonic bonding, and casting and still partially melting polymer directly onto other nonwoven fabrics. Bonding methods of any number known to those skilled in the art, including but not limited to extrusion laminating by bonding to one side of the nonwoven fabric in a closed state or by directly depositing the melt blown fiber nonwoven onto the nonwoven fabric. It can also be combined by. Such and other suitable laminate manufacturing methods are disclosed in US Pat. No. 6,013,151 and US Pat. No. 5,932,497.

Test Methods

Rheological Optical Characterization

This method is suitable for measuring the onset of flow induced crystallization in the polymer melt. In summary, turbidity is described in US Pat. No. 6,199,437 and various wall shear stresses can be obtained using apparatus and methods discussed further in Kumaraswamy, G. et al., Review of Scientific Instruments, 70 , 2097. Measure as a function of time in σ _w ). For simplicity, the following steps are used:

1) determining a suitable sample evaluation temperature by:

a) The primary transition temperature (i.e. crystal melting point) is measured using differential scanning calorimetry (DSC). Suitable instruments are available on model TAQ1000 from TA Instruments, New Castle, Delaware, USA.

b) The sample is heated to 200 ° C. using a DSC apparatus and held at this temperature for 2 minutes and then the sample is cooled to 20 ° C. lower than the temperature determined in step a.

c) At the temperature of step b, determine the time required for the exothermic peak using a DSC instrument in T4P mode. This is comparable to the time required for a 50% increase (t ⁰ _{1 / 2T} ) in turbidity in seconds at this temperature.

d) should reduce the sample temperature was 5 ℃ repeated isothermal determination of t ⁰ _1/2.

e) Repeat step d until the last evaluation temperature is less than 110 ° C.

f) steps c - using the data collected from e to determine the temperature at which the curve of t ⁰ _{1 / 2T} for temperature and t ⁰ _1/2 is 10,000 seconds (approximately 2.8 hours). This temperature is the resting t ⁰ _1/2 of the sample (ie shear force-σ _w = 0) which will be used in step 3.

2) heating the sample to a temperature of 200 ° C. using the apparatus described in Kurmaswamy, et al. And holding the sample at this temperature for 2 minutes prior to any evaluation of step 3.

3) t _1/2 is measured using the apparatus and method described in Kumarraswamy et al. Under the following conditions (measurement should be carried out at the resting t ⁰ _1/2 temperature determined in step 1). box):

Record the actual inlet pressure measured by the pressure transducer for each condition and associate the recorded pressure with the actual σ _w using the following equation:

σ _w = ΔP * d / (2L)

here,

ΔP = drop in pressure across the shear instrument (atmospheric pressure at the experimental conditions used is the inlet pressure at the transducer since it is negligibly small)

d = depth of the flow channel of the shearing machine (suitable for 0.5 mm)

L = length from the pressure transducer to the outlet of the shearing device (suitable for 8.3 cm)

4) Drawing a curve comparing t _1/2 with σ _w .

5) determine the values of t ^{_{1/2 (t 0 .11 1/2}} ) at 0.11 MPa of σ _w and t ^{0 .11} _1/2: t ⁰ _1/2 further comprising: calculating a ratio of.

Melting temperature

Melting temperatures can be suitably measured using differential scanning calorimetry, as described in ASTM standard method D1505. Record the highest melt temperature observed for each. For blends in which the average melt temperature is reported, the average melt temperature is the linear weighted (weight percent of constituent resin or resin fraction in the blend) average of the highest melt temperature of the component resin or fraction. For example, when characterizing the composition of the blend using TREF (see below), the highest melting temperature of each fraction should be measured and the highest temperature of the fractions weighted according to the fraction composition determined from the TREF analysis, resulting in the blend's melting temperature. Should be determined. In addition, the fraction melt temperature is combined using data on the composition to determine the melt temperature of the blend components identified through other analytical methods (eg gel permeation chromatography or nuclear magnetic resonance).

Melt flow rate

Melt flow rate can be suitably measured using ASTM standard method D1238. For blends in which the average melt temperature is reported, the log melt flow rate can be calculated by determining the linear weighted (weight percent of constituent resin or resin fraction in the blend) average of the log melt flow rate of the constituent resin or fraction. For example, when characterizing the composition of the blend using TREF (see below), the melt flow rate of each fraction must be determined and its log melt flow rate must be determined. The log melt flow rate of the fraction is then weighted according to the fraction composition determined from the TREF analysis to determine the log melt flow rate of the blend. The melt flow rate of the blend is determined via launch.

Furtherance

Temperature Rising Elution Fractionation (TREF)

TREF analysis is suitable for separating polymer samples into fractions representative of their components. In summary, the sample is dissolved and the solution is dispensed onto the carrier surface (e.g., column packing material suitable for chromatography) and then the dispensed solution is slowly cooled to precipitate the polymer fractions in the reverse order of solubility (i.e. minimal Soluble fraction is precipitated first). After the sample has cooled, the flowing solvent is passed over the precipitated polymer to redissolve the polymer. Separate portions of the polymer solution formed thereby are collected and further analyzed (e.g., gel permeation chromatography to determine the average molecular weight of the fraction (suitable for weight average molecular weight, ie light scattering detector or number average molecular weight). A suitable detector such as a capillary viscometer or both may be used) or nuclear magnetic resonance to measure the degree of branching in the fraction). The temperature of the solvent slowly increases to increase its solubility so that the collected fractions represent a portion of the original sample of different solubility. This solubility difference may be due to differences in properties such as molecular weight, degree of branching, and the like.

Sample

1) Collect 20 g of the polymer material sample to be tested.

Way

Suitable TREF methods and apparatus are described in Wild, L., "Advances in Polymer Science", Vol. 98 (1990) Springer-Verlag Heidelberg, Germany, pp 1-47.

Mounting of textile samples

For each sample tested, 10-12 fibers are randomly selected and separated from the bundle of extruded fibers. The fibers are then taped to a paper coupon so that the ends of the tape and fibers overlap with the back side of the coupon. Be careful not to expand or deform the fibers in any way.

Fiber shape and diameter

The shape of the fiber can be suitably sized by microscopic examination of the cross section of the extruded fiber and such cross section is taken perpendicular to the long axis of the fiber.

The fiber diameter of the circular fibers described in the examples can be suitably measured using a Zeiss Axioskope (Carl Zeiss, Milan, Italy) microscope with color video cameras and display monitors. . With the fibers in focus (mounted as described above) under a 40X objective lens and a 1X eyepiece, the diameter of the fibers is measured on the monitor in inches with calipers. The microscope is calibrated for this magnification using a 1 mm scale divided into 100 scales manufactured by Graticules LTD, Tonbridge, UK.

Denier

Denier can be suitably measured using ASTM standard method D1577.

Tensile properties

Low Speed Tensile Properties (Fibers)

Slow tensile properties are measured according to ASTM standard D3822. An MTS Synergy ™ 400 tensile tester (MTS Systems Corporation, Eden Prairie, MN) with 10 Newton load cells and pneumatic grips may also be used. The test is performed at a crosshead speed of 200% per minute on a single fiber sample with a gage length of 2.54 cm. Coupon loaded fibers are loaded into the tester grip. The paper is then cut off to avoid disrupting the test results. Pull the sample and break it. The report includes peak load, final tensile stress, elongation at break (elongation at break), Young's modulus, and energy per volume at break. The stress at 30% strain is considered the yield stress.

Low Speed Tensile Properties (Nonwoven Materials)

Slow tensile properties are measured according to EDANA (European Disposables and Nonwovens Association) standard method 20.2-89. An MTS Synergy ™ 400 tensile tester (MT Systems Corporation, Eden Prairie, MN) with 100 Newton load cells and pneumatic grips may also be used. The following conditions are used:

Activated tensile properties

The activated tensile properties are described in co-pending US patent application Ser. No. 10 / 377,070, filed under the name of Anderson et al. On February 28, 2003, entitled "Ring Rolling Simulation Press". Measurements can also be made using the disclosed devices and methods. The following setting conditions are used, corresponding to a maximum strain of 500 seconds ⁻¹ :

Fluff level test

This method is used as a quantitative prediction of the abrasion resistance of non-woven materials or laminate materials and weighs 907 g (2 pounds) with 320 grit sandpaper using a Sutherland Ink Rub Tester. This is done by wearing a piece of test material of 11.0 cm x 4.0 cm. Loose microfibers are collected on a weighed adhesive tape to determine the amount of coarse microfibers collected per unit area. Details of this method are given in US Patent Application 2002/0119720 A1. As practiced for the evaluation of the material of the present invention, the release liner disclosed in the method of the '720 application for fluff levels was released from American Coated Products, Gionsville, Indiana, USA. Paper) is available.

The following examples illustrate the practice of the invention but are not intended to be limiting. Further embodiments and variations within the scope of the claimed invention will be apparent to those skilled in the art. Accordingly, the scope of the present invention should be considered in view of the following claims and is understood not to be limited to the method described in the specification. The overall objective is to determine the effects of variations in melt flow rate and the broad composition on the overall balance of the properties of spunbond webs and fibers made from custom polypropylene / propylene random copolymer (PP / RCP) blends, especially with regard to their stretching properties. To prove.

Example 1

This example includes propylene / ethylene random copolymers of different crystallinity (as measured by average melt temperature) and melt flow rate of one polypropylene homopolymer and have a broad composition and broad molecular weight distribution. The preparation of miscible (or at least extremely compatible) PP / RCP blends is described.

Blends were prepared by dry blending the polypropylene homopolymer resin with the RCP resin in a polymer extruder and then mixing to ensure that the blend components are optimally melt blended with each other. Although the analysis was not performed at all, it is considered that the resin also contains an effective amount of a subcomponent (for example, an antioxidant). The extruder used in the examples below is a Warner & Pfleiderer (30 mm diameter, length to diameter ratio of 40: 1) co-rotating twin screw extruder set at 31.4 rad / s (300 RPM), The heating zones were set at 180, 195, 205, 200 and 213 ° C, respectively, so that the average melting temperature was 229 ° C. All materials were allowed to flow down to a mass throughput of 9 kg / hour (20 pounds / hour). Pellets of blended resin were obtained by extruding strands through a water bath to cool and crystallize this material and then pass the pelletizer to cut the strands into pellets.

Examples of two-component blends prepared through the above methods and their components are listed in Table 1 below. The ingredients are Exxon Mobile Company, Japan Polypropylene Company, Tokyo, Japan, Ato-Fina Chemicals, Houston, Texas, USA and Solvay Polyolefins Europe, Brussels, Belgium. Commercially defined narrowly defined Ziegler-Natta or metallocene-catalyzed polypropylene homopolymers or RCP resins supplied by Europe. These are described in Table 1 by their melting point (which is a measure of average composition) and their melt flow rate (which is a measure of average molecular weight). Binary blends are described by their average melt flow rate and their average melting point (calculated as the weighted average of the melting points of the constituent materials), as determined by the standard mixture rules applied for miscible polymers. The resulting blend has a wide range of melt flow rates and composition distributions. Also included in Table 1 are the molecular characteristics of various other PP based grades.

1. Metallocene propylene / ethylene random copolymer of Japan Polypropylene (Tokyo, Japan)

2. Control Rheology-Polypropylene Homopolymer from Exxon (Exxon Chemical Chemical Company, Houston, TX)

3. Metallocene Polypropylene Homopolymer from Atopina Chemicals, Houston, TX

4. Exxon's metallocene polypropylene homopolymer

5. Ziegler-Natta-propylene / ethylene random copolymer of Solvay Polyolefins Europe (Brussels, Belgium)

6. Ziegler-Natta propylene homopolymer of Basel Polyolefins, Wilmington, Delaware, USA

7. Propylene Homopolymer of Ziegler-Natta Controlled Rheology from Basel Polyolefins, Wilmington, Delaware

8. Type 2 Blend

9. Type 1 Blend

The melting point T _M and melt flow rate (as log, ie log MFR) of each of these materials is shown in FIG. 1. The blend is drawn on a line connecting the properties of the resin component. As can be seen, these lines have two significantly different slopes. Lines 10 and 12 have a negative slope and represent blends (eg blends I and J) which are referred to herein as type 1 blends. Type 2 blends are shown in FIG. 1 as lying along lines 14 and 16, each with a positive slope (eg, blends G and H). Certain type 2 blends (eg blend G) represent blends according to the present invention. As can also be seen in FIG. 1, blends with similar T _M and log MFR can be prepared as either type 1 or type 2 blends (compare blends H and J with blends G and I). As will be seen in subsequent examples, the type 1 blend and type 2 blend (ie, the blend of the present invention) have very different properties.

Example  2: fiber spinning

Pure or mixed material was melt spun into fibers using two extruder systems, each extruder being a single-screw extruder. The extrusion rate from each extruder to the spinpack is controlled by a metered melt pump feeding a four hole spin pack (Hills Incorporated, West Melbourne, FL). The extruder was set to deliver the resin or resin blend to the melt pump at a temperature of about 230 ° C. In all the embodiments, the spin pack is provided with spinnerets for round holes and distribution plates for sheath-core cross sections. In the one-component fibers of this example, the same resin is used in both extruders in a case where the sheath-to-core ratio is approximately 50:50. The extruder / melt pump / spinpack system is mounted on a height adjustable platform. In this example, the mass throughput was kept constant at approximately 0.8 grams / hole / minute and the spin line length was kept constant at a distance of approximately 1.78 meters. The molten filament exits the spinneret into a quench cabinet located directly below the spin pack and is a height adjustable air resistance device that uses compressed air at high pressure to produce an air stream that draws around the filament. Lower A series of fiber diameters are collected by varying the inlet pressure of the air gun and the type of air gun.

The fibers were spun at various drop ratios and collected for tensile testing. The fiber spinning speed is defined by the amount of drop imparted to the fiber phase in the spinning process. This is directly related to the final diameter of the spun fibers for a given known polymer throughput. The following examples, summarized in Table 2, provide results for test fibers comprising some of the polymer compositions listed in Table 1.

1. Extruded at approximately 1200 m / min

2. Extruded at approximately 1700 m / min

Example  3: Immiscibility  Inclusion of Ingredients

This example describes the preparation and evaluation of samples incorporating fractions of immiscible components (polymers of the second subgroup).

Dispersions of such second subgroups of polymers in various polypropylene resins or resin blends were prepared as described in Example 1 above. Table 3 illustrates the composition of the dispersion of this example.

1. Adflex Z104S from Basel Polyolefins, Wilmington, Delaware, USA.

2. 05862N HDPE from Dow Chemical Company, Midland, Michigan, USA.

This dispersion was then spun into fibers at an extrusion rate of about 1700 meters / minute using the apparatus described in Example 2 above. Table 4 lists the various mechanical properties of the fiber.

Example  4: Kinetic Characteristics of Flow-Induced Crystallization

This example compares the kinetic properties of flow induced crystallization of type 1 and type 2 blends. In this example, the melt of type 1 blend (blend G) and type 2 blend (blend I) was subjected to various wall shear stresses (σ) using the method described by the rheological-optical characterization in the test method section below. _w ) was evaluated for turbidity during flow through the shear instrument. As will be appreciated, crystallization from the melt will lead to an increase in turbidity from the solid phase produced therein which is related to the amount of crystallization and can be measured. Differential scanning calorimetry was used to measure the melting temperature of each of the Type 1 and Type 2 blends giving a comparable rate of rest (σ _w = 0) crystallization. As a result, the rheological-optical data was collected at a temperature of 145 ° C for type 1 blends and at 142 ° C for type 2 blends. The results are shown in FIG. 2, where t _1/2 (time in seconds required for a 50% increase in turbidity) is compared with the wall shear stress ((σ _w )) in mega Pascals (MPa). have. As can be seen in FIG. 2, the curve 201 for the type 1 blend is 1) a value of t ⁰ _1/2 substantially equal to the value of the type 2 blend and 2) σ _w slightly greater than 0.11 MPa. It represents a rapid increase in turbidity at the value of (a rapid decrease at t _1/2 ). On the other hand, the curve for the type 2 blend shows that the change in t _1/2 monotonically decreases over the range of σ _w evaluated.

Example  5: nonwoven fabric manufacturing

The following examples illustrate the extrusion and formation of nonwoven materials on a spunbond nonwoven pilot line. Nonwoven materials having the compositions and properties described in Table 5 were fabricated on a pilot scale on a 1 meter wide spunbond pilot line using a slot jet attenuation system. The web was prepared at a mass throughput of about 0.3 grams / hole / minute and thermally consolidated in one of two different bonding patterns. Pattern S has a rhombic junction, with a total junction area of 14% and a junction density of 32 joints / cm 2. Pattern A has a square bond site with a total bond area of 15% and a bond density of 26 bonds / cm 2.

Table 6 lists the mechanical properties of this web.

All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference, and no citation of any document should be construed as an admission as prior art relating to the invention.

While specific embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, all such changes and modifications that fall within the scope of the invention are intended to be included in the appended claims.

Claims (13)

(a) a first polypropylene, preferably metallocene poly, having an average melting temperature T _M1 of preferably 110 ° C. to 135 ° C. and a melt flow rate MFR ₁ of preferably 5 g / 10 min to 25 g / 10 min. Propylene; And (b) a second polypropylene having an average melting temperature T _M2 of preferably 135 ° C. to 165 ° C. and a melt flow rate MFR ₂ of preferably 25 g / 10 min to 50 g / 10 min. It includes; The average melt temperature T _Mb is from 125 ° C. to 160 ° C. and the melt flow rate MFR _b is from 10 g / 10 minutes to 40 g / 10 minutes, T _M1 <T _Mb <T _M2 , MFR ₁ <MFR _b <MFR ₂ , Polymer blend, characterized in that MFR ₂ / MFR ₁ ≧ 2.0. The method of claim 1, T _M2 - Polymer blend characterized in that T _M1 ≧ 10 ° C. The method of claim 1, And wherein the weight ratio of said first polypropylene to said second polypropylene is from 1: 4 to 4: 1. The method according to any one of the preceding claims, And wherein said first polypropylene is a metallocene random copolymer of propylene and ethylene. The method according to any one of the preceding claims, Wherein said first polypropylene is a copolymer of propylene and a comonomer selected from the group consisting of ethylene and C ₄ to C ₂₀ α-olefins. The method according to any one of the preceding claims, And the second polypropylene is a copolymer formed by polymerization of propylene and C ₄ to C ₂₀ α-olefins. Having a first haze half-life measured under quiescent conditions and a second haze half-life measured at a wall shear stress of 0.11 MPa, wherein the ratio of the second haze half-life to the first haze half-life is greater than 0.33, preferably Polypropylene material, characterized in that the ratio is greater than 0.5. (i) a polymeric material according to any of the preceding claims; And (ii) supplements Polymer mixture comprising a. The method of claim 8, Wherein said adjuvant comprises a polymer other than said first and second polypropylene, said polymer being selected from the group consisting of polymers insoluble in said polymer blend and polymers soluble in said polymer blend. A fiber comprising the polymeric material according to any one of the preceding claims. The method of claim 10, The fiber is a bicomponent fiber, wherein the bicomponent fiber further comprises a second component comprising a first component which is a polymeric material according to any one of the preceding claims and which is a compatible resin. A nonwoven material comprising the fiber of claim 11. An absorbent article comprising the nonwoven material of claim 12.

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