HOT MELT PRESSURE SENSITIVE POSITIONING ADHESIVE (II)

Abstract: The present invention is a hot melt pressure sensitive positioning adhesive for use with an absorbent article. The adhesive contains from 6 to less than 15 percent by weight of a selectively hydrogenated block copolymer of styrene and (butadiene and/or isoprene) and styrene (e.g. styrene-ethylene/butylene styrene -SEBS; or styrene-ethylene/propylene styrene -SEPS) in blend with a selectively hydrogenated styrene-isoprene-styrene-isoprene block copolymer (styrene-ethylene/propylene-styrene-ethylene/propylene - SEPSEP) and, optionally, an amorphous ethylene/propylene copolymer. The blend comprises at least 6 wt.% if the total of blend, tackifying resin and plasticizer.

Description: HOT MELT PRESSURE SENSITIVE POSITIONING ADHESIVE (II) Field of the Invention This invention relates to hot melt pressure sensitive positioning adhesives for use with absorbent articles which are based on blends of hydrogenated block copolymers of styrene and butadiene or isoprene and exhibit improved viscosity and viscosity/temperature profile . Background of the Invention Positioning adhesives are used on disposable articles such as sanitary napkins, incontinent pads, bed pads, feminine pads, panty shields and diaper inserts, where an adhesive layer is used to attach the article to a woven fabric substrate such as a supporting undergarment or bed sheet. The positioning adhesive is commonly applied to a release liner and transfer coated to the garment facing surface of the disposable article. The positioning adhesive must be capable of attaching to the undergarment to hold the article in place without transferring to or otherwise being deposited on the undergarment. Furthermore, the adhesive must not discolor, damage, or disturb the fibers of the garment. The positioning adhesive must be a pressure sensitive adhesive that has an application viscosity that permits it to readily flow onto and partially penetrate the particular surface to which it is applied. It must have good bond strength and high tack for initial placement of the article on the undergarment but also must have the ability to avoid loss of adhesion over time due to temperature conditions. Finally, these articles are sometimes used for long periods of times at body temperature and they can have the drawback that the hot melt adhesive gradually softens and penetrates into the undergarment to which the article is adhering. In this case, the adhesive force greatly increases and the cohesive force is reduced. This causes the adhesive layer to suffer cohesion breakdown when the article is removed and some adhesive remains on the undergarment. Prevention of this deposit of adhesive on the undergarment is accordingly a necessary prerequisite for a successful positionable hot melt adhesive composition. Block copolymers of styrene and dienes such as butadiene or isoprene have been used for a number of years in positionable hot melt adhesive formulations. More recently, the material of choice for such adhesives in feminine care applications has been selectively hydrogenated block copolymers of styrene and butadiene such as KRATON G-1650 polymer (KRATON is a trademark) , which is a commercially available selectively hydrogenated styrene-butadiene-styrene block copolymer. With the term "selective hydrogenation" is meant that primarily the butadiene block is hydrogenated. Butadiene that has been polymerised by 1,4-addition yields "ethylene" units upon hydrogenation and butadiene that has been polymerised by 1, 2-addition yields "butylene" units. Therefore, selectively hydrogenated styrene- butadiene-styrene block copolymers are commonly referred to as styrene-ethylene/butylene-styrene (SEBS) block copolymers . The amount of butadiene that has been polymerised by 1 , 2-addition, relative to the total amount of polymerised butadiene, is commonly referred to as "vinyl content before hydrogenation" or "the butylene content" . In case of isoprene, the vinyl content before hydrogenation is the total amount of isoprene that has been polymerised by either 1, 2-addition or 3, 4-addition, relative to the total amount of polymerised isoprene. The vinyl content of a selectively hydrogenated styrene- (butadiene and/or isoprene) -styrene block copolymer can vary widely. In case of butadiene the vinyl content before hydrogenation is typically at least 18%, preferably at least 25%. Typically, a vinyl content before hydrogenation of up to 50% is sufficient. According to one preferred embodiment, the vinyl content before hydrogenation is up to 45%. It may, however, also be desirable to use block copolymers having a vinyl content before hydrogenation of more than 50%, such as m the range from greater than 50 to 90%. Formulations based on these SEBS block copolymers have been found to have excellent adhesion to fabrics like cotton and nylon and have the advantage that they leave no residue after peeling. The application viscosity, i.e. melt viscosity, of formulations using these polymers is acceptable but it would be advantageous to have a positionable adhesive formulation which has a lower melt viscosity in order to be able to lower the application temperature. This reduces the risk of degradation, char forming, and filter plugging. This also results in energy and cost savings, decreases maintenance costs, and reduces the amount of odor due to any volatiles coming from the adhesive formulation. The present invention provides such an improved positionable hot melt adhesive formulation. Summary of the Invention The present invention is a hot melt pressure sensitive positioning adhesive for use with an absorbent article. The adhesive comprises: (a) from 6 to less than 15 percent by weight of the total of (a) , (b) and (c) of a blend of (l) from 40 to 95% by weight of the blend of a selectively hydrogenated styrene- (butadiene and/or isoprene) -styrene block copolymer; and (ii) from 5 to 60% by weight of the blend of a selectively hydrogenated styrene-isoprene-styrene- isoprene block copolymer; and (iii) from 0 to 40% by weight of the blend of an amorphous ethylene/propylene copolymer having a weight average molecular weight of 9,000 to 30,000; and (b) from 50 to 80 percent by weight of the total of (a), (b) and (c) of a tackifying resin which has an aromaticity such that the MMAP cloud point is at least 45 °C; and (c) from 5 to 35 percent by weight of the total of (a) , (b) and (c) of a plasticizer. Detailed Description of the Invention One of the primary components of the positioning adhesive composition of the present invention is the above-described hydrogenated block copolymer that has two polystyrene endblocks and a saturated or hydrogenated polybutadiene and/or polyisoprene midblock. This conventional hydrogenated base block copolymer provides the primary load bearing capability of the adhesive composition. It is important that the polymer be hydrogenated so that the structural integrity of the polymer is preserved even if outside forces that cause degradation are encountered. The block copolymer may be hydrogenated as generally described in the prior art, preferably so as to reduce at least 90 percent of any olefinic double bonds in the polymer chains. Suitably at least 50 percent, preferably at least 70 percent, and more preferably at least 90 percent, most preferably at least 95 percent of the original olefinic unsaturation is hydrogenated. Anionic polymerization of conjugated diene hydrocarbons with lithium initiators is well known as described in U.S. Patents Nos . 4,039,593 and Re. 27,145 which descriptions are incorporated herein by reference. Polymerization commences with a monolithium, dilithium, or polylithium initiator which builds a living polymer backbone at each lithium site. Typical living polymer structures containing polymerized conjugated diene hydrocarbons are : X-B-Li X-A-B-Li X-A-B-A-Li Li-B-Y-B-Li Li-A-B-Y-B-A-Li wherein B represents polymerized units of one or more conjugated diene hydrocarbons such as butadiene or isoprene, A represents polymerized units of one or more vinyl aromatic compounds such as styrene, X is the residue of a monolithium initiator such as sec-butyllithium, and Y is the residue of a dilithium initiator such as the diadduct of sec-butyllithium and m-diisopropenylbenzene . Some structures, including those pertaining to polylithium initiators or random units of styrene and a conjugated diene, generally have limited practical utility although known in the art . In general, the polymers useful in this invention may be prepared by contacting the monomer or monomers with an organoalkali metal compound in a suitable solvent at a temperature in the range from -150 °C to 300 °C, preferably at a temperature in the range from 0 °C to 100 °C. A polar additive ("structure modifier") is used to increase the vinyl content in case the solvent used is apolar. Particularly effective polymerization initiators are organolithium compounds having the general formula: RLi wherein R is an aliphatic, cycloaliphatic, alkyl- substituted cycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbon radical having from 1 to 20 carbon atoms. Suitable solvents include those useful in the solution polymerization of the polymer and include aliphatic, cycloaliphatic, alkyl-substituted cycloaliphatic, aromatic and alkyl-substituted aromatic hydrocarbons, ethers and mixtures thereof. Suitable solvents, then, include aliphatic hydrocarbons such as butane, pentane, hexane and heptane; cycloaliphatic hydrocarbons such as cyclohexane and cycloheptane; alkyl-substituted cycloaliphatic hydrocarbons such as methylcyclohexane and methylcycloheptane; aromatic hydrocarbons and (alkyl- substituted aromatic) such as benzene, toluene and xylene; and ethers such as tetrahydrofuran, diethylether and di-n-butyl ether. The hydrogenation of these polymers may be carried out by a variety of well established processes including hydrogenation in the presence of nickel catalysts such as Raney Nickel, noble metal catalysts such as those containing platinum and/or palladium and soluble transition metal catalysts. Suitable hydrogenation processes which can be used are ones wherein the diene- containing polymer or copolymer is dissolved in an inert hydrocarbon diluent such as cyclohexane and hydrogenated by reaction with hydrogen in the presence of a soluble hydrogenation catalyst. Such processes are disclosed in U.S. Patent Nos . 3,113,986, 4,226,952 and Reissue 27,145, the disclosures of which are herein incorporated by reference. The polymers are preferably hydrogenated in such a manner as to produce hydrogenated polymers having a residual unsaturation content in polydiene blocks of less than about 1 percent, and most preferably as close to 0 percent as possible, of their original unsaturation content prior to hydrogenation. A titanium catalyst such as disclosed in U.S. Patent No. 5,039,755, which is herein incorporated by reference, may also be used in the hydrogenation process. The molecular weights of linear polymers or unassembled linear segments of polymers such as mono-, di-, or triblock, or the arms of star polymers before coupling are conveniently measured by Gel Permeation Chromatography (GPC) , where the GPC system has been appropriately calibrated with polystyrene homopolymer standards (ASTM D 3536) . For anionically polymerized linear polymers, the polymer is essentially monodisperse (weight average molecular weight/number average molecular weight ratio approaches unity) , and it is both convenient and adequately descriptive to report the "peak" molecular weight of the narrow molecular weight distribution observed. Usually, the peak value is between the number and the weight average. The peak molecular weight is the molecular weight of the main species shown on the chromatograph. For polydisperse polymers the weight average molecular weight should be calculated from the chromatograph and used. The materials used in the columns of the GPC are styrene-divinyl benzene gels or silica gels. The solvent is tetrahydrofuran and the detector is a refractive index detector. As discussed above, the adhesive of the present invention contains from 6 to less than 15 percent by weight of a selectively hydrogenated block copolymer of styrene and (butadiene and/or isoprene) and styrene (e.g. styrene-ethylene/butylene styrene - SEBS; or styrene- ethylene/propylene styrene - SEPS) in blend with a selectively hydrogenated styrene-isoprene-styrene-isoprene block copolymer (styrene-ethylene/propylene - styrene- ethylene/propylene - SEPSEP) and, optionally, an amorphous ethylene/propylene copolymer. Typically, the blend comprises at least 6 %wt (preferably at least 8 %wt) of the total of blend, tackifymg resin and plasticizer to get the best pressure sensitive adhesive properties and for the adhesive to be sufficiently cohesive. It is preferred that the maximum amount of the polymer blend is less than 15 percent by weight in order to keep the viscosity of the adhesive sufficiently low for the positioning adhesive application. More polymer than 15 weight percent basis components (a)+(b)+(c) can be used and good adhesion properties will be obtained but the viscosity will be unnecessarily increased. The base triblock copolymer must have a sufficient molecular weight and polystyrene content to be useful for pressure sensitive adhesives. Generally, the number average molecular weight should be in the range from 65,000 to 300,000 g/mol. If the molecular weight is less than 65,000 then the polymer loses its pressure sensitive adhesive properties. If the molecular weight is more than 300,000, then the polymer is less useful for adhesive applications. The polystyrene content preferably ranges from 10 to 40 percent by weight because this confers the right balance of cohesion and processability to the polymer. The four block SEPSEP copolymer preferably has a number average molecular weight of 65,000 to 130,000 g/mol, a polystyrene content of 13 to 30% by weight, and a polystyrene block molecular weight of 6,000 to 15,000 g/mol. Amorphous polyalpha-olefins are low molecular weight, saturated homopolymers, like atactic homopropylene (APP) or copolymers of ethylene/propylene (APE) like the EASTOFLEX grades E-1003, E-1060 or E-1200, or propylene/ hexene copolymers (APH) like D-127 from Eastman or terpolymers such as ethylene/propylene/butene like VESTOPLAST grades from Creanova (formerly Huels) (EASTOFLEX and VESTOPLAST are trademarks) . Amorphous polyalpha-olefins are well known to be incompatible with styrene-ethylene/butylene-styrene block copolymers. However, it has been discovered that amorphous ethylene/propylene copolymers (APE) have acceptable compatibility with hydrogenated styrene-isoprene block copolymers such as styrene-ethylene/ propylene-styrene and styrene-ethylene/propylene-styrene-ethylene/propylene block copolymers. Viscoelascic studies by dynamic mechanical analysis (Universal VI.10B TA instrument) show that blends of SEPS/APE (65/35%) show only one peak tan delta value with a significant shift from the peak tan delta value of the ethylene/propylene mid-block of SEPS. Indeed, the peak tan delta of KRATON G-1730 is at -41 °C, the peak tan delta of APE E-1060 is at -14 °C, and the peak tan delta of the 65/35% by weight blend is at -34 °C. Theoretical calculations of the peak tan delta value with the Fox equation (see Handbook Of Pressure Sensitive Adhesive Technology, Don Satas, Van Nostrand Rheinhold, 1989 in Chapter 13, Thermoplastic Rubbers, page 369), which assumes complete compatibility, give a value of the peak tan delta of the blend of -32 °C. This value is very close to the measured one (-34 °C) . This indicates a fair compatibility between SEPS and APE. In comparison, a blend KRATON G-1657 (SEBS) /E-1060 (65/35%) gives the following values: the peak tan delta of KRATON G-1657 is -41 °C, the peak tan delta of E-1060 is +3 °C, and the peak tan delta value of the blend is -37 °C. Theoretical peak tan delta value as calculated by the Fox equation gives a value of -29 °C. This clearly indicates the poor compatibility of SEBS and APP. It has now been found that the improved compatibility between SEPS and APE can be used to achieve some improvements in adhesive properties and particularly a higher peel on fabrics like cotton and nylon. The APE used in this invention typically have a weight average molecular weight in the range of from 9,000 to 30,000 g/mol and is determined on a Water 150 °C GPC that was calibrated with low-Mw polyethylene standard, and a hot-melt viscosity between 200 and 25,000 cPs at 190 °C. Further, these copolymers have a Ring and Ball softening point (ASTM D 36) between 110 °C and 140 °C. They are used in an amount of 0 to 40% by weight of the total polymer. If APE is used, the preferred range is 5 to 40% by weight. Such products are best described for example in the Eastman publications WA-4D and WA-67 and in Advances in Pressure Sensitive Adhesive Technology-2 , edited by Don Satas in 1995. It is known that one method to characterize tackifying resin compatibility is by determination of cloud points in suitable solvent systems. From the cloud point values obtained, the resin may be characterized as being aliphatic, aromatic, or a combination of both, polar or nonpolar, and having a high or low molecular weight. Hydrocarbon resins display wide variation in cloud point values and thus the cloud point concept is a useful method to characterize hydrocarbon resins. MMAP cloud point is a well known measure of aromatic solubility and determines the aliphatic/aromatic character of the resin. The lower the MMAP cloud point value, which is expressed in degrees centigrade, the more aromatic is the resin. A 1:2 mixture of methylcyclohexane and aniline is used as the solvent system in the MMAP cloud point determination. A standard weight of resin is dissolved in the solvent at high temperature and allowed to cool with mixing. The temperature at which the resin begins to separate out as an extra phase is determined to be the MMAP cloud point. This may be seen in the mixture as a cloudiness in the previously clear solution. Suitable tackifiers may be selected from the group consisting of compatible C5 hydrocarbon resins, hydrogenated C5 hydrocarbon resins, styrenated C5 resins, C5/C9 resins, styrenated terpene resins, fully hydrogenated or partially hydrogenated C9 hydrocarbon resins, rosins esters, rosins derivatives and mixtures thereof. The tackifying resin must have an MMAP cloud point that is at least 45 °C in order for the polymer/resin blend to be compatible. Commercially available hydrocarbon tackifying resins for the present invention include PICCOTAC 95 (MMAP = 95 °C) as aliphatic resin, REGALREZ series, like REGALREZ 1085 (85 °C) or REGALREZ 6108 (54 °C) and REGALITE series, like REGALITE V-1100 (48 °C) or REGALITE S-260 (59 °C) . REGALREZ 3102 resin (MMAP = 24 °C) does not work with these polymers because a phase stable blend cannot be achieved (PICCOTAC, REGALREZ and REGALITE are trademarks) . Suitable plasticizers include low aromatic content hydrocarbon oils that are paraffinic or naphthenic in character (e.g. have a carbon aromatic distribution < 5%, preferably < 2%, more preferably 0% as determined according to DIN 51378) . Those products are commercially available from Shell Oil Company, like SHELLFLEX, CATENEX, ONDINA oils, KAYDOL oil from Witco, or TUFFLO oils from Arco (SHELLFLEX, CATENEX, ONDINA, KAYDOL and TUFFLO are trademarks) . Other plasticizers include compatible liquid tackifying resins like REGALREZ R-1018. Other plasticizers might also be added, like olefin oligomers; low molecular weight polymers (< 30,000 g/mol) like liquid polybutene or liquid polyisoprene; copolymers, like liquid styrene/isoprene copolymers or hydrogenated styrene/isoprene copolymers; liquid alpha- olefin polymers; vegetable oils and their derivatives, paraffin and microcrystalline waxes. It is known in the art that various other components can be added to modify e.g. the odor and/or the color of the adhesives. Antioxidants and other stabilizing ingredients can also be added to protect the adhesive from degradation induced by heat, light and processing or during storage. Several types of antioxidants can be used, either primary antioxidants like hindered phenols or secondary antioxidants like phosphite derivatives or blends thereof. Examples of commercially available antioxidants are IRGANOX 565 from Ciba-Geigy (2.4-bis-(n- octylthio) -6- ( 4-hydroxy-3, 5-di-tertiary-butyl anilino) - 1,3,5-triazine) , IRGANOX 1010 from Ciba-Geigy (tetrakis- ethylene- (3, 5-di-tertiary-butyl-4-hydroxy-hydrocinna- mate)methane) and POLYGUARD HR from Uniroyal (tris-(2,4- di-tertiary-butyl-phenyl) phosphite) (IRGANOX and POLYGUARD are trademarks) . The adhesive composition of the present invention typically has a viscosity of 100 to 10,000 cPs at 177 °C, preferably from 600 to 6,000 cPs at 177 °C. The adhesive typically exhibits no transfer after being peeled away from a fabric. The adhesive composition is used in articles such as disposable diapers, sanitary napkins, bed pads, incontinent pads, surgical drapes, plasters and bandages . EXAMPLES KRATON G-1650 is a selectively hydrogenated styrene- butadiene-styrene block copolymer having a number average molecular weight of 109,000, a polystyrene content of 30 percent by weight, and polystyrene block molecular weight of 10,000. KRATON G-1730 is a selectively hydrogenated styrene-isoprene-styrene-isoprene block copolymer having a weight average molecular weight of 103,000, a polystyrene content of 21.5 percent by weight, and polystyrene block molecular weight of 6700. E-1060 is an amorphous ethylene/propylene copolymer (APE) having a Ring and Ball Softening Point of 135 °C, a hot-melt viscosity of 6,000 cPs at 190 °C, and a weight average molecular weight of 23,300. Example 1 All the ingredients were compounded in a Z-blade mixer. Then the samples were put in beaker in an oven at 180 °C. Once molten, the adhesive was poured onto a Mylar sheet and cast to obtain a thickness of 2 mils (50 μm) . Prior to testing, the samples were conditioned at 23 °C and 50% RH (relative humidity) for 24 hours. Standard peel, tack and cohesion tests were carried out on these formulations. To assess the right functionality of the adhesive, specific adhesion tests on fabrics were performed, namely to evaluate the adhesion of the positioning adhesive onto the undergarment. Cotton and nylon fabrics are the two reference materials used in these tests. The following peel adhesion tests on fabric were carried out : Peel adhesion initial: for cotton, the initial peel is preferred to be in the range of 200-500 g/lineal inch (77-193 N/m) . - Peel adhesion retention or aging test: the samples (fabric/adhesive/Mylar) are put in an oven at 40 °C/8 hours under a load of 160 g/sq. in. (24.8 g/cm 2 ). Peel adhesion is determined after 1 hour conditioning at 23 °C and 50% RH . Occurrence of adhesive transfer to the fabric is reported as "none" or "transfer". Adhesive transfer: the samples (fabric/adhesive/Mylar) are put in oven at 40 °C/24 hours under a load of 800 g/sq. in. (124 g/cm 2 ) . Peel adhesion is determined after 1 hour conditioning at 23 °C and 50% RH . Occurrence of adhesive transfer is also reported as "none" or "transfer". The SAFT (shear adhesion failure temperature) was measured by 1" x 1" (2.5 x 2.5 cm) Mylar to Mylar lap joint with a 1 kg weight. SAFT measures the temperature at which the lap shear assembly fails under load. Rolling Ball Tack (RBT) is the distance a steel ball rolls on the adhesive film with a standard initial velocity (Pressure Sensitive Tape Council Test No. 6) . Small numbers indicate aggressive tack. Holding Power (HP) is the time required to pull a standard area (1/2 in. x 1/2 in.) (1.3 x 1.3 cm) of tape from a standard test surface (steel, Kraft paper) under a standard load (1 kg), m shear at 2° (Pressure Sensitive Tape Council Method No. 7) . Long times indicate high adhesive strength. 180° peel was determined by Pressure Sensitive Tape Council Method No. 1. Large numbers indicate high strength when peeling a test tape from a steel substrate. Polyken probe tack (PPT) was determined by ASTM D-2979. Loop tack (LT) was determined using PSTC-5 loop tack method. High numbers for PPT and LT indicate aggressive tack. T-peel is measured by ASTM D-1876. Table 1 below shows the results for the polymers alone and blended together. PICCOTAC 95 is a trademark for an aliphatic hydrocarbon tackifying resin which is manufactured by Hercules. V 1100 is a hydrogenated mixed cyclic aromatic tackifying resin which is manufactured by Hercules. TUFFLO 6056 oil is a plasticizmg oil which is manufactured by ARCO . Formulation F-2 based on KRATON G-1730 has adhesion initial properties close to KRATON G-1650 but with a much lower hot-melt viscosity. However, it exhibits transfer and is thus unacceptable. Formulation F-3, based on KRATON G-1730 and APE, has higher adhesion on fabrics than the KRATON G-1650 reference but unfortunately exhibits also transfer. Formulation F-4, a blend of KRATON G-1730, KRATON G-1650, and APE, shows a low hot- melt viscosity coupled with excellent adhesion on fabric without adhesive transfer. Formulation F-5, which is also a blend of KRATON G-1730, KRATON G-1650, and APE with a higher percentage of KRATON G-1730 than F-4 shows adhesive transfer. This indicates that the polymers can be blended to achieve a successful formulation but only in a limited ratio. Too much KRATON G-1730 causes transfer. A very important advantage of adding KRATON G-1730, i.e., to reduce the viscosity, is also proven here. Table 1 Tabl e 1 ( cont ' d ) T indicates transfer to the fabric MT indicates a medium transfer ST indicates a slight transfer Example 2 Table 2 shows the hot-melt viscosity in function of the temperature. The hot-melt viscosity is measured with a Bookfield Thermocell DV11 - RV following ASTM D-3236-73. The formulation containing the blend KRATON G-1650, G-1730, and APE (F-4) has a much lower hot-melt viscosity than the reference formulation based solely on KRATON G-1650 (F-l) . Formulation F-4 can be coated at much lower temperature than the KRATON formulation. - I S Table 2 formulation F-l. Example 3 In this example, blends of various tackifying resins with varying MMAP cloud point values were tested with KRATON G-1650 for phase stability. The results are shown in Table 3 below. Table 3 Compatibility SBC/resin blends in function of the aromaticity of the resin as defined by the MMAP cloud point in °C I = INCOMPATIBLE C = COMPATIBLE Example 4 The conditions for samples preparation and testing are given in example 1. In this example, two other polymers were evaluated in blends with KRATON G-1730 and APE. Polymer A is a styrene-ethylene/butadiene-styrene block copolymer with 33% polystyrene content, a weight average molecular weight of about 280 000, and a vinyl content before hydrogenation of about 70%. Polymer B is a styrene-ethylene/propylene-styrene block copolymer with 35% polystyrene content and a weight average molecular weight of about 270 000. As seen in Table 4, formulation F-7 shows that when polymer A is compounded with KRATON G-1730 and APE, the hot-melt viscosity (HMV) is decreased considerably compared to the formulation F-6 without KRATON G-1730. Moreover, formulation F-7 has higher adhesion on cotton and nylon, much higher than the reference formulation F-l of example 1 based on KRATON G-1650. This effect is due to the synergy of KRATON G-1730 and APE. Polymer B, compounded with KRATON G-1730 and APE in formulation F-9, shows higher adhesion on nylon and cotton than the reference formulation F-l in example 1. When compounded with KRATON G-1730, the hot-melt viscosity is decreased considerably compared to formulation F-8 without KRATON G-1730. Table 4 HMV = Hot melt viscosity.

Claims: C L A I M S 1. A hot melt pressure sensitive positioning adhesive for use with an absorbent article which comprises: (a) from 6 to less than 15 percent by weight of the total of (a), (b) and (c) of a blend of (i) from 40 to 95% by weight of the blend of a selectively hydrogenated styrene- (butadiene and/or isoprene) styrene block copolymer; and (ii) from 5 to 60% by weight of the blend of a selectively hydrogenated styrene-isoprene-styrene- isoprene block copolymer; and (iii) from 0 to 40% by weight of the blend of an amorphous ethylene/propylene copolymer having a weight average molecular weight of 9,000 to 30,000; and (b) from 50 to 80 percent by weight of the total of (a) , (b) and (c) of a tackifying resin which has an aromaticity such that the MMAP cloud point is at least 45 °C; and (c) from 5 to 35 percent by weight of the total of (a) , (b) and (c) of a plasticizer. 2. The adhesive of claim 1 wherein the block copolymer of (ii) has a number average molecular weight of 65,000 to 130,000, a polystyrene content of 13 to 30% by weight, and a polystyrene block molecular weight of 6,000 to 15,000. 3. The adhesive of claim 1 wherein the block copolymer of (i) has a number average molecular weight of 65,000 to 300,000 and a polystyrene content of 10 to 40% by weight. 4. The hot melt adhesive of claim 1 wherein the viscosity of the adhesive is from 100 to 10,000 cPs at 177 °C and the adhesive exhibits no transfer after being peeled away from a fabric. 5. The adhesive of claim 3 wherein the viscosity of the adhesive is from 600 to 6000 cPs at 177 °C.

Inventors: DE KEYZER NOEL RAYMOND MAURICE, STONER CAROLYN ANN, DE KEYZER, NOEL, RAYMOND, MAURICE, STONER, CAROLYN, ANN
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 2000
Main classification: A61L15
IPC codes: A61L15, C09J11, C09J153