MXPA06007586A - Elastomer compositions and method of making them - Google Patents

Abstract

Compositions of high and low performance elastomer are formed using a process that chemically reacts some of the high and low performance elastomers together to form a graft copolymer. The elastomeric compositions provide intimately mixed elastomeric compositions which are thermodynamically stable and do not phase separate. The elastomeric compositions exhibit a variety of improved properties compared to simple blends of the same high and low performance elastomers in the same weight proportions. The elastomeric compositions are useful for producing films, fabrics, and laminates for use in a wide variety of personal care and medical articles.

Description

COMPOSITIONS OF ELASTOMER AND METHOD TO MAKE THEM Field of the Invention The invention is directed to high performance and low performance elastomer compositions, and to films and fabric layers formed using the elastomeric compositions.

Background of the Invention High performance thermoplastic elastomers are elastomers which when formed into a film, yarn or similar article can be extended to a stretched length and retracted without experiencing a substantial loss in retraction force at an intermediate stretched length (lower) . Although these elastomers typically have useful properties of high strength, low hysteresis, low creping and low stress relieving, these are expensive relative to other elastomers and thermoplastic polymers in general.

Low performance thermoplastic elastomers are elastomers which, when formed in a film, yarn or similar article, can be extended to a stretched and retracted length but essentially lose their retraction force at an intermediate (lower) stretched length. Even though these elastomers are typically less expensive than Higher performance elastomers, these exhibit higher levels of hysteresis, creping and tension relaxation when stretched.

The high and low performance elastomers have been mixed together in several attempts to create blends which retain the performance characteristics of high performance elastomers to the extent possible, while saving on material costs. Mixing does not result in mixtures of elastomers having suitable hysteresis, creping, stress ratio or other properties. One reason for this is Gibb's free mixing energy that is positive, due to the high interfacial tension between the high performance elastomer molecules and the low performance elastomer. Gibb's free energy of mixing, or? G, is defined as the Gibb's free energy of the elastomer mixture minus the sum of Gibb's free energies of the components before mixing at a reference temperature.

When Gibb's free mixing energy is positive, thermodynamics favor phase separation over intimate mixing of the two elastic polymer components. Frequently, one of the components forms a continuous phase, while the other component forms a discontinuous phase of droplets or domains dispersed within the continuous phase. This phase separation adversely affects the elastic properties of the mixture and may result in melting insensitivity during processing, and in a non-uniform measurement and non-uniform physical appearance of the film or filament structure being produced. The tendency for phase separation decreases with the Gibb's free mixing energy approaching zero, and intimate mixing is favored when the Gibb's free mixing energy is less than zero.

Therefore, there is a need or desire for an elastic polymer composition including a high performance elastomer and a low performance elastomer, which combine the performance properties of the high performance elastomer with the cost benefits of the low performance elastomer. . More specifically, there is a need or desire for an elastic polymer composition that includes a high performance elastomer and a low performance elastomer, which has a lower Gibb's free energy of mixing than the simple blend of the same high performance elastomer. and the same low performance elastomer, in the same weight ratios, at ambient (storage) and elevated temperatures (mixing and processing). There is also a need or a desire for the film and fabric layers formed to use such an improved elastic copolymer composition.

Synthesis of the Invention The present invention is directed to an elastomer composition, including a high performance elastomer and a low performance elastomer, in which it has a Gibb's free mixing energy and improved elastic performance characteristics compared to a simple blend of the high performance elastomer and the same low performance elastomer, in the same weight proportions. The elastomer composition is formed by chemically reacting at least a small percentage of the high performance elastomer with at least a small percentage of the low performance elastomer to form high and low performance elastomer graft copolymer molecules. The graft copolymer molecules are compatible with the remaining (ungrafted) polymer molecules of both the high performance elastomer and the low performance elastomer, and promote the intimate mixing of the elastomer components. The invention is also directed to the fabric and film layers formed using the elastomeric polymer composition.

The resulting elastomeric composition is thermodynamically stable, more intimately mixed, and the high and low performance elastomers are more compatible. The composition combines the performance characteristics of the high performance elastomer with the cost benefits of the low performance elastomer.

With the foregoing in mind, it is a feature and an advantage of the invention to ide an imed elastomeric composition that includes a high performance elastomer and a low performance elastomer.

It is also a feature and an advantage of the present invention to ide film and fabric layers formed using the imed elastomeric composition.

Definitions The terms "elastic" and "elastomeric" are used interchangeably to mean a material that is generally capable of recovering its shape after deformation when the deforming force is removed. Specifically, as used herein, the elastic or elastomeric is intended to be that erty of any material which with the application of a pressing force allows the material to be stretched to a pressed and stretched length which is at least about 50% greater than the unstressed and relaxed length and which will cause the material to recover at least 40% of its elongation with the release of the elongation stretch force after the first stretch cycle. A hypothetical example which will satisfy this definition of an elastomeric material will be a 1-inch sample of a material which is elongated to at least 1. 50 inches, and which, when lengthened to 1.50 and released, will recover to a length of no more than 1.30 inches after the first stretch cycle. Many elastic materials can be stretched for much more than 50% of their relaxed length and much will recover to their original relaxed length substantially with the release of the stretching elongation force.

The term "recover" refers to a contraction of the stretched material with the termination of a pressing force that follows the stretching of the material by the application of the pressing force, as illustrated in the previous example.

The term "stretch percent" refers to the ratio determined by measuring the increase in one dimension during stretching, dividing that value by the original dimension and multiplying the result by 100. % stretch = (Stretched dimension minus original dimension) x ^ 00 Original dimension The term "polymer" includes homopolymers, copolymers, such as, for example, block, graft, random and alternating copolymers, terpolymers, etc. and mixtures and modifications thereof. The term "polymer" also includes all possible geometric configurations of the molecule. These configurations include but are not limited to isotactic symmetry as syndiotactic and random.

The term "mixture" refers to a combination of two or more polymers. The term "high performance elastomer" refers to an elastomer of has a hysteresis value of 25% less, suitably 20% less, determined according to the hysteresis test method described herein.

The term "low performance elastomer" refers to an elastomer having a hysteresis value of more than 25%, suitably 40% more, determined according to the hysteresis test method described herein.

The term "graft copolymer" as applied to high and low performance elastomers includes all di-block copolymers in which one of the blocks is a molecular segment or high performance elastomer molecule and the other of the blocks is a molecular segment or low performance elastomer molecule. The term includes a) copolymers in which a molecular segment or high performance elastomer molecule is chemically bound to a column of a low molecular weight elastomer molecule or segment; b) copolymers in which a molecular segment or low performance elastomer molecule is chemically bound to the column of a molecular segment or high performance elastomer molecule and c) copolymers in which a molecular segment or high performance elastomer molecule and a low molecular segment or molecule of elastomer are chemically bound end-to-end.The term "Gibb's free energy", expressed as the symbol "G", is a thermodynamic expression of the potential energy within a polymer system represented by the equation: G = H - TS Where H is the enthalpy of the polymer system, T is the absolute temperature, and S is the entropy in the polymer system Gibb's free energy and enthalpy can each be expressed in units of energy (eg calories), energy per unit mass (eg calories / gram), or energy per mole (eg calories / mole).

Entropy can be expressed in units of energy by degree of temperature (eg calories / K), energy per unit mass per degree of temperature (eg calorie / gram K), or energy per mole per degree of temperature (eg calories / mol-K).

The term "enthalpy", expressed as the symbol "H", is the sum of the total internal energy (U) of a polymer plus the product of its volume (V) and the absolute pressure (P) otherwise expressed as: H = U + PV The enthalpy values for the various substances are commonly found in tabulations of thermodynamic properties. Enthalpy values, and changes in enthalpy can also be determined and calculated using known techniques.

The term "entropy", expressed as the "S" symbol, is a measure of the extent of chance within the polymer system. When chance within the polymer system is cause or allowed to increase (for example, when the molecular orientations become more random) the entropy increases. When the chance within the polymer system caused by the decrease (for example, when the molecules are more oriented or aligned more) the entropy decreases. Entropy and changes in entropy can be determined using known techniques.

Brief Description of the Drawing Figure 1 is a register-record scheme of tension relieving modules versus time for the elastomer samples described in examples 8, 13-15, and 19-22.

Detailed Description of Current Preferred Incorporations The present invention is directed to an elastomeric composition and to film and fabric layers formed therefrom. The composition includes a high performance elastomer, a low performance elastomer, and a high performance elastomer and low performance elastomer graft copolymer. The graft copolymer promotes intimate mixing and thermodynamic stability within the composition. The composition can include about 5-95% by weight of the high performance elastomer and about 5-95% by weight of the low performance elastomer, suitably about 20-80% by weight of the high performance elastomer and about 20% by weight. -80% by weight of the low performance elastomer, particularly about 30-70% by weight of the high performance elastomer and about 30-70% by weight of the elastomer of low performance The composition may also include additional elastomeric or non-elastomeric polymers. When other polymers are present, the high performance elastomer and the low performance elastomer should constitute at least about 50% by weight of the total polymer in the composition, suitably at least about 70% by weight, particularly at least around 90% by weight.

The high performance elastomer is one which exhibits a hysteresis value of 25% less adequately than 20% less particularly 15% less, or 10% less determined according to the hysteresis test method described herein. To perform the hysteresis test, the high performance elastomer by definition must have sufficient integrity and elasticity to form a film that stands alone having a thickness of 25 microns, which can be stretched at least 100% its initial length and allowing recovery. High performance elastomers include without limitation styrenic block copolymers, for example styrene-diene block copolymers and styrene-olefin sold under the trade name KRATON® by Kraton Polymers L.L.C.

Suitable styrene-diene copolymers include the copolymers of di-block, tri-block, tetra-block and other block copolymers and may include without limitation block copolymers of styrene-isoprene, styrene-butadiene, styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-isoprene-styrene-isoprene, and styrene-butadiene-styrene-butadiene. Suitable styrene-olefin block polymers include without limitation styrene-diene block copolymers which diene groups have been totally or partially hydrogenated selectively including, without limitation, styrene- (ethylene-propylene) block copolymers, styrene - (ethylene-butylene), styrene- (ethylene-propylene) -styrene, styrene- (ethylene-butylene) -styrene, styrene- (ethylene-propylene) -styrene- (ethylene-propylene), and styrene (ethylene-butylene) -styrene- (ethylene-butylene). In the above formulas, the term "styrene" indicates a block sequence of styrene repeat units; the terms "isoprene" "butadiene" indicate block sequences of diene units; the term "(ethylene-propylene)" denotes a block sequence of ethylene-propylene copolymer units "(ethylene-butylene)" denotes a block sequence of ethylene-butylene copolymer units. The styrene-diene or styrene-olefin block copolymer should have a styrene content of from about 10 to about 50% by weight, suitably from about 15 to about 25% by weight, and should have a molecular weight of average number of at least about 40,000 grams / mol, suitably about 60,000 to about 110,000 grams / mol.

The low performance elastomer is one which exhibits a hysteresis value of more than 25%, suitably 40% more, particularly around 50-75%, determined according to the hysteresis test method described herein. To perform the hysteresis test, the low performance elastomer by definition must have sufficient integrity and elasticity to form a film that separates itself having a thickness of 25 microns, which can be stretched at least 100% its initial length and allow it to recover. Suitable low performance elastomers include without limitation the single site catalyzed alpha olefin-ethylene copolymer resins having a density of about 0.915 grams / cm 3 or less, suitably about 0.860-0.900 grams / cm 3, particularly about 0.865 -0.895 grams / cm3. The term "single-site catalyzed" includes without limitation alpha-olefin-ethylene copolymers formed using constrained geometry or metallocene catalysis. Examples of the single site catalysts include bis (n-butylcyclopentadienyl) titanium dichloride, bis (n-butylcyclopentadienyl) zirconium dichloride, bis (cyclopentadienyl) scandium chloride, bis (indenyl) zirconium dichloride, bis (methylcyclopentadienyl) dichloride ) titanium, bis (methylcyclopentadienyl) zirconium dichloride, cobaltocene, cyclopentadienyl titanium trichloride, ferrocene, hafnocene bichloride, isopropyl (cyclopentadienyl-1-fluoroenyl) zirconium dichloride, molybdocene dichloride, niquelocene, niobocene bichloride, ruthenocene, titanocene dichloride , zirconocene chloride hydrate, zirconocene bichloride, among others. A more exhaustive list of such compounds is included in U.S. Patent No. 5,374,696 to Rosen et al. And assigned to The Dow Chemical Company. Such compounds are also discussed in U.S. Patent No. 5,064,802 issued to Stevens et al. And also assigned to The Dow. However, numerous other single site catalyst systems are known in the art; see, for example, U.S. Patent No. 5,539,124 issued to Etherton et al .; 5,554,775 granted to Krishnamurti and others; 5,451,450 issued to Erderly et al. And the Encyclopedia of Chemical Technology of Kira-Othemer, Fourth Edition, volume 17, Olefin Polymers page 765-767 (from John Wiley &Sons 1996); whose full contents of these patents have been incorporated herein by reference.

The single site catalyzed alpha olefin-ethylene copolymer can be formed using a C3 to C12 alpha-olefin comonomer and suitably formed using a comonomer of butane, hexene or octene. The amount of the comonomer is usually between about 5-25% by weight of the copolymer and can vary depending on how much comonomer is required to achieve the desired density. Normally, higher comonomer quantities and / or large comonomer molecules result in lower densities. The low performance elastomer can have a number average molecular weight of at least about 30,000 grams / mol, suitably from about 50,000 to about 110,000 grams / mol, and can have a melt index of about 0.5-30 grams / 10 minutes at 190 ° C, suitably around 12-15 grams / lOmin, measure using Condition E ASTM D-1238. The suitable single site catalyzed alpha olefin-ethylene copolymers are made and sold by the Dow Chemical Company under the trade names AFFINITY and ENGAGE, and by Exxon-Mobil Chemical Company under the trade names EXACT and EXCEED.

To form the elastomeric composition of the invention, the high performance elastomer and low performance elastomer parts are graft copolymerized to form graft copolymers of a) a high performance elastomer on a low performance elastomer column, b) a low performance elastomer on a high performance elastomer column and / or o) high and low performance elastomers joined end to end. Graft copolymerization can be accomplished by a variety of techniques.

A suitable graft copolymerization technique is the solid state cutting spray. The high and low performance elastomers are fed together or separately into one or more hoppers of a twin screw extruder of high torsional force equipped with co-rotating screws. The co-rotating screws are adjusted with kneading and cutting elements as well as conveyor elements. The extruder includes a heating system, and a fluid or other cooling system means to remove excess heat generated due to friction. The high and low performance elastomers are mixed in the extruder under high cut at a temperature that is below the melting or softening temperature of both elastomer polymers. Friction and heat are generated by the kneading and cutting elements in a part of the extruder, causing a chain break ("visup") of the individual high and low performance elastomer polymer molecules to form free radicals and / or rupture of residual double bonds, obstruction of hydrogen atoms or other compatible mechanisms. The cooling of the extruder subsequently causes the free radicals to recombine. Some of the free radicals in the high performance elastomer molecules combine with the free radicals of the low performance elastomer molecules to form graft copolymer molecules having high and low performance elastomer chains. The resulting mixture of the high performance elastomer, the low performance elastomer and the graft copolymer is then extruded as the elastomeric composition of the invention.

The thus formed graft copolymer molecules can constitute from about 0.1 to about 10% of the combined weight of the high performance elastomer, the low performance elastomer and the graft copolymer, suitably from about 0.5 to about 7.5% of the weight combined particularly around 1.0 to around 5.0% of the combined weights. The parts of the graft copolymer molecules that resemble the high performance elastomer are compatible with the remaining amount of the unreacted high performance elastomer. The parts of the graft copolymer molecules that resemble the low performance elastomer are compatible with the remaining amount of the low performance elastomer.In one embodiment, the graft copolymer can be formed in an amount greater than that stated above, resulting in a master or concentrate charge rich in the graft copolymer. The master batch or concentrate can then be further diluted with amounts of high performance elastomer and / or low performance elastomer, to provide an elastomeric composition having a level of graft copolymer within the declared ranges, and / or a predetermined optimum level of graft copolymer.

In the resulting elastomer composition, the high and low performance elastomer and the graft copolymer are intimately mixed together at their interfaces, as compared to similar mixtures devoid of the graft copolymer. The elastomer composition has sufficient thermodynamic stability so that the components remain intimately mixed in their masks during subsequent processing and use. As a result, the The elastomer composition of the invention forms films, fabrics and other articles which exhibit increased strength, improved elastic recovery, less hysteresis, less creping and better stress relaxation compared to a simple mixture of the same high performance elastomers and low in the same proportions by weight, devoid of the graft copolymer.

As indicated above, the Gibb's free energy of an elastomer or an elastomer composition can be determined from the following equation: G = H - TS Where G is Gibb's free energy, and can be expressed as calories. H is the enthalpy, and can be expressed as calories. T is the absolute temperature and can be expressed as K, and S is the entropy and can be expressed as calories / K.

Whether an elastomeric composition exhibits or thermodynamic stability depends not only on the current value of Gibb's free energy, but rather of the difference in Gibb's free energy between the elastomeric composition and the high and low performance elastomers before mixing. Assuming a constant reference temperature, this difference in Gibb's free energy (for example Gibb's free energy of mixing) can be expressed as follows: ? G =? H - T? S Where ? G is the change in Gibb's free energy of the elastomer composition in relation to the Gibb's free energy of the unmixed components at a reference temperature,? H is the change in the enthalpy of the elastomer composition in relation to the enthalpy total of the components not mixed at the reference temperature, T is the absolute reference temperature,? s is the change in entropy of the elastomer composition in relation to the total entropy of the components before mixing.

Due to the presence of the compatibilizing graft copolymer molecules, the elastomer composition of the invention has a lower Gibb's free energy of mixing (a lower? G) than a simple mixture containing the same high and low performance elastomers. the same proportions and amounts of weight. Suitably, Gibb's free energy of mixing (? G) is not more than about zero, and is suitably less than zero. When the Gibb's free energy of mixing (? G) is almost zero, the components will remain mixed to the extent that they can be mixed together, but will exhibit no natural tendency to intimate mixing or phase separation. When the Gibb's free energy of mixing (? G) is less than zero, intimate mixing allows the elastomer molecules to transit from the high energy state to a lower energy state, causing the release of heat. Thermodynamics favor intimate mixing over phase separation, and the components have a natural tendency to mix together and remain mixed. When the thermodynamics of the elastomeric composition of the invention are described, the term "components" includes not only high and low performance elastomers, but also graft copolymers and (where applicable) any additional polymer ingredients. These ratios are true at the reference temperatures of 300 K and 500 K, for the elastomer composition of the invention.

The cutting spray useful for forming the elastomer composition of the invention can be carried out using a suitable twin screw reaction / mixing extruder. Suitable twin screw extruders are available in various sizes from Werner-Pfleiderer Corporation, Berstorff, and other companies. The twin screw extruders are equipped with heating and cooling capabilities in a plurality of zones located along the length of the extruder. The twin screws can also be equipped with various arrangements of transport elements, kneading elements and cutting elements to provide an elastomeric composition with optimum properties. The temperature in the extruder can be controlled individually in several zones, and can vary from about 25 ° C to about 250 ° C, suitably from about 40 ° C to about 150 ° C. The temperatures in the reaction zone (cutting spray) are typically lower than between about 25-100 ° C properly and around 40-90 ° C. The temperatures down from the mixing zone (approaching the matrix) may be higher to facilitate melting and mixing of the components. Internal pressures can range from about 50 to 150 atmospheres.

Other techniques can also be employed to form the elastomeric composition of the invention, including forming the graft copolymer molecules of high and low performance elastomers. For example, the visitation to form free radicals can also be achieved thermally (with fewer cuts) by using higher temperatures inside the extruder. Free radicals can also be generated at the lower extruder temperatures with the help of a peroxide catalyst. Free radicals can also be generated in solution with the help of the catalyst peroxide. In each case at least some of the free radicals recombine to form the graft copolymer while others may recombine to form the elastomer molecules of higher or lower performance.

As explained above, other polymers or included in the elastomeric composition of the invention can be added. Such other polymers include non-elastomeric polymers such as various polyethylenes, polypropylenes and other polyolefins, as well as elastic polymers that do not fall within the definitions of high and low performance elastomers provided herein. When present, the other polymers should constitute less than about 50% by weight of the elastomer composition, suitably less than about 3% by weight, suitably from about 10% by weight. The other polymer can be added to the elastomeric composition before or after the graft copolymerization process. If the other polymers are included in the graft copolymerization process, they can also undergo the arrest, generation of free radical, and graft copolymerization together with molecules of a high and low performance elastomer. If one or more other polymers are already compatible with the high and low performance elastomer, these may alternatively be added after completing the graft copolymerization.

The elastomeric composition of the invention can also be combined with a particulate filler, from which the elastomeric composition can be formed into a film, and stretched-thinned to form a microporous breathable film which is permeable to water vapor and essentially impermeable to liquid water. The term "breathable" refers to a material having a water vapor transmission rate (WVTR) of at least about 1200 grams / m2-24 hours suitably of at least about 2000 grams / m2-24 hours, suitably of at least about 3000 / m2-24 hours using the water vapor transmission rate test as described herein. When used, the particulate filler may constitute about 25-75% by weight of the elastomeric composition, suitably about 35-65% by weight. To form the breathable film, the filled elastomeric composition is formed into a film for which then it is disoriented in at least one direction to around 2-7 times its initial dimension in that direction and then it is relaxed. Stretching causes the voids to form around the filler particles. The gaps are surrounded by thin polymer membranes which create a tortuous path from one side of the film to the other.

Generally, the filler particles have average particle sizes of about 0.5-8 microns, suitably about 1-2 microns. Suitable fillers include calcium carbonate (CaCO3), various kinds of clay, silica (SiO2), alumina, barium sulfate, sodium carbonate, talc, magnesium sulfate, titanium dioxide, zeolites, aluminum sulfate, powders of type of cellulose, diatomaceous earth, calcium oxide, magnesium oxide, aluminum hydroxide and the like. The filled particles are suitably inorganic but alternatively they can be organic. Organic fillers include cellulose, cyclodextrins and cage molecules (for example nanoestirated silsesquioxane oligomeric polyhedra) The elastomeric polymer csition of the invention can be used to form a wide variety of articles including films, yarns, fibers and fabrics such as spunbonded nonwoven fabrics, melt blown nonwoven fabrics and other woven and nonwoven materials. for which the elastomeric performance and the reduced costs are important or desired.

The elastomeric csition of the invention can be used to form films for use in a variety of applications, including without limitation the absorbent articles for personal care, medical absorbent articles, medical garments, covers, caps, sterilization casings and Similar. When the elastomeric film includes a particulate filler as described above, and is stretched, the film can be made breathable to water vapor. The elastomeric film can be laminated to a fabric such as an elastic nonwoven fabric, to form a film / nonwoven laminate. The laminate can be a stretched-attached laminate (formed while the film is in a stretched state and the non-woven fabric is relaxed), a narrowed and bonded laminate (formed while the non-woven fabric is narrowed-stretched and the film is relaxed), or a bonded and stretched and tapered laminate (formed while the film is in a stretched state and the non-woven fabric is tapered-stretched in the same direction as the film). The laminate layers can be bonded together thermally as ultrasonically or using an adhesive.

The elastomeric film and / or a nonwoven laminate can be used in articles for care personal absorbers, which typically include a liquid-permeable body-side liner, an outer liquid-impervious cover (with adequate water vapor breathing capacity) and an absorbent core therebetween. The elastomeric film can be perforated and used as a side-to-body liner. The rolled laminate of elastomeric / non-woven laminate especially breathable can be used as the outer cover. Examples of absorbent articles for personal care include, without limitation, diapers, underpants, adult incontinence articles, articles for women's hygiene and the like.

The elastomeric csition of the invention can be used to form a fibrous nonwoven fabric or other fabric in which the fibers themselves are csed of the elastomeric csition, such fabrics are inherently elastic. The elastomeric fabrics can therefore be formed by joining them to an elastic or inelastic film to form the fabric laminate. Again, elastomeric fabrics and laminates can be used in a wide variety of personal care articles and medical articles as indicated above.

Test Procedures Test for hysteresis measurement The hysteresis of a film sample is determined using a Sintech 1 / S or 2 / S apparatus equipped with a TESTWORKS software to record data. The elastomeric composition is formed into a film having a thickness of about 25 microns. The film is cut into strips each having a width of 3 inches and a length of 6 inches. Both ends of the film strip are gripped on the opposing jaws of the apparatus so that an inch of the length on each end of the film is held within the jaws and 4 inches of length are available for stretching.

Each film strip is stretched at a rate of 500 mm / per minute per 100% (increasing the exposure length from 4 to 8 inches) and the area under the curve (representing the force displacement X) was measured and recorded as the "charge energy". The film strip is then allowed to recover to a length where the stretching force is zero. During retraction, the area under the curve is again measured and recorded. This is the "discharge energy".

The hysteresis is determined according to the following equation: % hysteresis = Load less discharge energy x 100% Load energy The procedure for measuring Gibb's free mixing energy.

The Gibb 's free energy of mixing can be measured or calculated according to procedures known in the art. A known procedure involves the use of the Flory-Huggins Theory. This procedure is described in Rosen, Fundamental Principles of Polymeric Materials, Second Edition, John Wiley & Sons, Inc. (1993), pages 85-94, and is incorporated herein by reference.

Procedure to determine the load loss (% LL) and the inclination.

The load loss (% LL) and its inclination are determined using a stress relaxation experiment with a film strip 1 inch wide by 7 inches long. The ends of the film strip are held in a Sintech 1 / S or 2 / S frame equipped with a TESTWORKS software to record data. The two inches of film strip length are held within the grip jaws on both ends and 3 inches of the length are exposed.

The test apparatus is maintained in a temperature controlled chamber of 100 ° F. The film strip is stretched at a rate of 40 inches per minute at an elongation of 50%, and is maintained in the stretched condition for 12 hours. The load as a function of time is measured and drawn, typically giving a curve which shows an exponential loss charge.

The load loss (% LL) with time (t) was determined from the following equation.

% LL = Load (t = 0) less load (t = 12 hours) X 100% Load (t = 0) Where t = time, hours The inclination which is constant over the period of time was determined from a logarithm (load) versus logarithm (time) plot, or from the following equation: m = -log [L (t) / L (0)] logarithm t Where m = tilt, L (t) = load at a time data (t) L (0) = start load at t = 0, and t = time Once the head loss and tilt have been determined, the letter L at any time data T can be determined from the following equation: L (t) = L (0) t-m Where m = magnitude (absolute value) of line inclination, t = time, L (t) = load at a given time, and L (0) = start charge at t = 0 Breathing capacity of water vapor rate (WVTR): A suitable technique for determining the value WVTR (water vapor transmission rate) of a film or laminate of the invention is the best process, standardized by the INDA (Association of the Non-Woven Fabrics Industry) standard, number IST- 70.4-99, entitled "STANDARD TEST METHOD FOR WASHING WATER STEAM TRANSMISSION" and is incorporated by reference herein. The procedure of the Association of the Non-Woven Fabrics Industry provides the determination of the water vapor transmission rate, the permeation of the film to water vapor and, for homogeneous materials the coefficient of water vapor permeability.

The test method of the Association of the Non-Woven Fabrics Industry is well known and will not be established in more detail here. However, the test procedure is summarized as follows. A dry chamber is separated from a wet chamber of a known humidity temperature by a permanent protection film and the sample material to be tested. The purpose of the guard film is to define a defined air separation and to quiet or quiet the air in the air gap while air separation is characterized. The dry chamber, the protective film and the humid chamber constitute a diffusion cell in which the test film is sealed. The sample holder is known as the Permatran-W Model lOOk manufactured by Mocon, Inc. of Minneapolis, Minnesota. A first test is made of the water vapor transmission rate of the protection film and the separation of air between an evaporator assembly that generates 100% relative humidity. The water vapor diffuses through the air separation and the protection film and is then mixed with a flow of dry gas which is proportional to the concentration of water vapor. The electrical signal is directed to a computer for processing. The computer calculates the air separation transmission rate and it keeps the film and the stores of said value for accurate use.

The transmission rate of the protection film and the air separation is stored in the computer as CalC. The sample material is then sealed in the test cell. Again the water vapor diffuses through the air gap to the protective film and the test material and is then mixed with a flow of dry gas sweeping the test material. Also, again, this mixture is taken to the vapor sensor. This information is used to calculate the transmission rate at which moisture is transmitted through the test material according to the equation: -I test material = test material, protective film, air separation_TR protective film, air separation Calculations: Water vapor transmission rate uses the formula: WVTR = Fpsat (T) RH / (Ap? At (T) (1-RH)) Where: F = The water vapor flow in cc / min. , Psat (T) = The density of water in saturated air at temperature T, RH = Relative humidity at specified locations in the cell, A = The cross-sectional area of the cell, and, - sat (T) = The vapor pressure of saturation of water vapor at temperature T.

For the purposes of this application, the test temperature for the above test is around 37.8 ° C, the flow is 100 cc / min, and the relative humidity is 60%. Additionally, the value for n is 6 and the number of cycles is 3.

EXAMPLES Samples of the elastomeric composition of the invention were prepared using a co-rotating twin screw extruder of high torsional force manufactured by Berstorff under the name PT-25, having a screw diameter of 25 millimeters and a length to diameter ratio of 26. The samples produced including KRATON 1652 (high performance elastomer) from Kraton Polymers LLC, and AFFINITY EG8200 (low performance elastomer) from Dow Chemical Company, in weight proportions of 70/30, 50/50 and 30/70 . The twin screw extruder included three zones - barrel cooling / heating along its length.

For each of the experimental samples, the first barrel zone (polymer feed) was maintained at a temperature of 107-190 ° C to facilitate the initial melting of the polymers. The first barrel zone It was equipped with the transport elements to carry the polymers forward.

The temperature in the second barrel zone was varied "complete cooling" (essentially below 100 ° C) and 215 ° C as shown in the table given below. The second barrel zone was equipped with high-cut "kneading" elements and reverse transport "seal" elements to facilitate increased pressure, cutting and breaking of some of the high performance elastomer and performance elastomer molecules low.

The temperature in the third barrel zone approaching the matrix was maintained at around 210 ° C. The third barrel zone was equipped with forward transport elements intended to build sufficient pressure behind the die, to facilitate extrusion through the die.

Table 1 indicates the results of the experiments. In each case, a mixture of the two elastomers was used as a control. Visibility and grafting of some of the elastomer molecules is suggested by a change in melt flow rate (in any direction) of the samples of the invention against the control. Changes in glass transition temperature also suggest a chemical reaction, with a glass transition temperature suggesting an attraction of improved mixing and compatibility between molecules. A lower percent load loss (% LL) and a less negative (more horizontal) slope indicates improved elastomeric performance.

Table 1 provides a representative summary of a work that has been done.

TABLE 1 * NA = Not available Figure 1 is a log-log diagram of stress relieving modulus (pounds per square inch) versus time (seconds) for the elastomer samples described in examples 8, 13-15 and 19-22. As illustrated in Figure 1, the inclination of the line is linear (for example constant) for each of the samples.

Although the embodiments of the invention described herein are presently preferred, various modifications and improvements can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated by the appended claims and all changes that fall within the meaning and range of equivalents are intended to be encompassed here.

Claims (20)

R E I V I N D I C A C I O N S

1. An elastomeric composition, comprising: a high performance elastomer; a low performance elastomer; a high and low performance copolymer.

2. The elastomeric composition as claimed in clause 1 characterized in that the copolymer of the high and low performance elastomers comprises a graft copolymer.

3. The elastomeric composition as claimed in clauses 1 or 2, characterized in that the high performance elastomer exhibits a hysteresis of 20% less.

4. The elastomeric composition as claimed in clauses 1 or 2 characterized in that the high performance elastomer exhibits a hysteresis of 15% or less.

5. The elastomeric composition as claimed in clauses 1 or 2 characterized in that the high performance elastomer exhibits a hysteresis of 10% or less.

6. The elastomeric composition as claimed in any of clauses 1 to 5 characterized in that the high performance elastomer comprises a styrene-diene block copolymer.

7. The elastomeric composition as claimed in any of Claims 1 to 5, characterized in that the high performance elastomer comprises a styrene-olefin block copolymer.

8. The elastomeric composition as claimed in clause 7 characterized in that the styrene-olefin block copolymer comprises a selectively hydrogenated styrene-diene block copolymer.

9. The elastomeric composition as claimed in any of clauses 1 to 8 characterized in that the low performance elastomer exhibits a hysteresis of 40% more.

10. The elastomeric composition as claimed in any of clauses 1 to 8 characterized because the low performance elastomer exhibits a hysteresis of 50-75%.

11. The elastomeric composition as claimed in any of Claims 1 to 10 characterized in that the low performance elastomer comprises a single site catalyzed alpha olefin-ethylene copolymer having a density of 0-910 grams / cm3 or less.

12. The elastomeric composition as claimed in clause 11 characterized in that the single site catalyzed alpha olefin-ethylene copolymer has a density of 0.860-0.900 grams / cm3.

13. The elastomeric composition as claimed in any of clauses 1 to 12, characterized in that it comprises: 5-95% by weight of the high performance elastomer; 5-95% by weight of the low performance elastomer; Y 0. 1-10% for that reason of the graft copolymer of high and low performance elastomers.

14. The elastomeric composition as claimed in clause 13 characterized in that it comprises 10-80% by that of the high performance elastomer, 20-80% by weight of the low performance elastomer, and 0.5-7.5% by weight of the graft copolymer .

15. The elastomeric composition as claimed in clause 13 characterized in that it comprises 10-80% by that of the high performance elastomer, 30-70% by weight of the low performance elastomer, and 1.0-5.0% by weight of the graft copolymer .

16. A film comprising the elastomeric composition as claimed in any of Clauses 1 to 15.

17. A laminate comprising the film as claimed in clause 16 and a non-woven fabric.

18. A fabric comprising at least one layer formed of the elastomeric composition of any of clauses 1 to 15.

19. An absorbent article for personal care comprising the film as claimed in clause 16, the laminate of clause 17 or the web of clause 18.

20. A medical article comprising the film of clause 16, the laminate of clause 17 or the fabric of clause 18.