AU5182600A - Articles formed by styrene-ethylene/butylene-styrene block copolymer/oil aqueous dispersions - Google Patents

Description

S&F Ref: 415019D1

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

oo* o oe Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Tactyl Technologies, Inc.

2595 Commerce Way Vista California 92083 United States of America Sebastian S Plamthottam Spruson Ferguson St Martins Tower 31 Market Street Sydney NSW 2000 Articles Formed by Styrene-Ethylene/Butylene-Styrene Block Copolymer/Oil Aqueous Dispersions The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c Articles Formed of Styrene-Ethylene/Butylene-Styrene Block Copolymer/Oil Aqueous Dispersions Background of the Invention This invention relates to articles formed from aqueous dispersions of styrene-ethylene/butylenestyrene block copolymers, preferably by dip forming.

Thin-walled, extensible articles such as gloves, condoms, and other products have long been made from natural rubber. In normal production, such articles are formed from natural rubber latex, a naturally occurring emulsion of rubber and water, with added stabilising agents and vulcanising chemicals. A form of the appropriate shape, previously coated with a coagulating solution in some cases, is dipped into the latex mixture once or several times to build up a layer of the desired thickness. The water is allowed to evaporate, leaving a solid rubber film. The film must be vulcanised to provide adequate mechanical and physical properties.

Natural rubber has many advantages in these applications, being strong and highly elastic and having good "tactility" or feeling to the user. Natural rubber has several shortcomings, such as .i 15 susceptibility to "pinholes" therethrough, rapid attack by ozone which causes scission cracking, and oxidative attack during storage which causes cracking and destroys the physical integrity of the product. Natural rubber is also not hypoallergenic due to the residual surfactants, vulcanising agents, stabilising agents, antioxidants, and/or protein materials in the rubber. Persons who are particularly susceptible to irritation or sensitisation, or who use the rubber products for extended periods of time, 20 may experience allergic reactions.

Various types of synthetic elastomeric polymer products have been developed for use in thin articles produced by dip forming. Synthetic rubber compositions may be dissolved in solvents to form a true solution, so that pinholes are much less likely to be present. Many available synthetic rubber compositions have various other shortcomings, including unacceptable tactility. While each such composition may meet some of the requirements, most do not have the required combination of strength, tactility, resistance to environmental damage, and hypoallergenicity required for many products such as examination and surgical gloves, condoms, and other medical products that are to come into contact with the human body.

An important advance in the art of synthetic elastomeric polymer products is described in US 112 900 and 5 407 715. These patents disclose the preparation of specific styrene-ethylene/butylenestyrene block copolymer solutions and their use in the dip forming of articles. The resulting articles have excellent elastomeric properties for use in gloves, condoms, and other products. They exhibit low incidence of pinholes, good resistance to environmental damage such as oxidation and ozonisation, and hypoallergenicity.

There is, however, always a need to further improve the manufacturability of articles made of such formulations and the process economics. The present invention fulfils this need, and further provides related advantages.

Summary of the Invention The present invention provides articles formed from styrene-ethylene/butylene-styrene aqueous dispersions and an approach for utilising those aqueous dispersions in the preparation of thin [I:DayUbIBC130859.doc:mef elastomeric articles. The articles have the desirable characteristics of comparable articles made from styrene-ethylene/butylene-styrene solutions, including excellent elastomeric properties, low incidence of pinholes, good resistance to environmental damage such as oxidation and ozonisation, and hypoallergenicity. The present approach is compatible with related technology such as the use of powders and powder-free techniques for improving the donnability of the articles. Additionally, the dispersion-based dip-forming manufacturing operation functions at greater rates for improved process economics, as compared with the prior approach of dip forming from styrene-ethylene/butylenestyrene solutions. Thicker layers or articles may be made in each dip-forming step. The manufacturing operation is also safer due to the absence of toxic solvents during the dip-forming process.

In accordance with the invention, an aqueous dispersion preferably comprises a dispersion medium comprising a mixture of water and a surfactant, and a plurality of particles dispersed in the dispersion medium. Each particle preferably comprises a mixture of an styrene-ethylene/butylenestyrene (styrene-ethylene/butylene-styrene) block copolymer, and an oil such as a mineral oil. Most preferably, the particles are of an average size of no greater than about 2pn. The styrene- 15 ethylene/butylene-styrene block copolymer, which may be formed of molecules of substantially the same molecular weight or mixtures of two or more molecular weights, preferably having weight average end block molecular weights of each of the end blocks of more than about 15 000Da.

The invention provides an elastomeric article comprising: a styrene-ethylene/butylene-styrene block copolymer, where the styrene-ethylene/butylene-styrene block copolymer has end blocks each having a weight average molecular weight of more than about 15 000Da; and an oil.

The aqueous dispersion may be used in a dip-forming method for manufacturing thin-walled articles. In accordance with this aspect of the invention, a method for the preparation of an elastomeric article preferably comprises the steps of furnishing an aqueous dispersion of the type l described, dipping a form into the aqueous dispersion and withdrawing the form from the aqueous dispersion, leaving a film of the dispersion on the form, and evaporating the water from the dispersion on the form and fusing the remaining polymeric material, leaving a coherent extensible film on the form. The aqueous dispersion used in the dip-forming method is preferably substantially free of nonaqueous solvents, but trace amounts that may be present are not detrimental in the dip-forming process, and may, in some cases, be beneficial in forming a coherent film.

The aqueous dispersion may be used in conjunction with other processing techniques. For example, the aqueous dispersion may be used in the coagulant dipping process that is utilised for natural latex rubber compounds. It also may be used, for example, in spray coating or slush moulding operations.

The resulting article has the desirable features associated with the styrene-ethylene/butylenestyrene block copolymers as described US 5 112 900 and 5 407 715. Additionally, the articles may be made much more quickly than possible with the solution-based approach described in these prior patents. In the manufacturing operation, the dispersion is normally made at a location which has apparatus for disposing of the potentially toxic solvent vapours evolved during preparation of the dispersion. The dip-forming operation may be performed elsewhere. Because there is no potentially P:Daytib\LIBCJ30859.doc:nef toxic solvent evolved in the dip-forming operation, there is little risk of injury to workers on the dipforming and drying line.

Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.

Brief Description of the Drawings Figure 1 is a block flow diagram of a preferred approach for practicing the invention; Figure 2A is a schematic microstructural view of an (styrene-ethylenelbutylene-styreneloil)-in- (water/surfactant) aqueous dispersion; Figure 2B is a schematic microstructural view of a (water/surfactant)-in-(styreneethylene/butylene-styrene/oil) aqueous dispersion; Figure 3 is a perspective view of a glove form; and Figure 4 is a perspective view of a male condom form.

15 Detailed Description of the Invention Figure 1 is a block flow diagram depicting a preferred approach for preparing an aqueous dispersion in accordance with the invention, and then for using that aqueous dispersion to prepare an article by dip forming.

A styrene-ethylene/butylene-styrene (styrene-ethylene/butylene-styrene) block copolymer is provided, numeral 20. The styrene-ethylene/butylene-styrene block copolymer is formed from an ethylene-butylene copolymer central block and polystyrene end blocks. The polystyrene end blocks each have a weight average molecular weight of at least about 15 000Da, and, more preferably, at least from about 18 000 to about 20 000Da. Because there is a relatively large amount of oil in the dip-forming solution, it is beneficial that styrene-ethylene/butylene-styrene block copolymer have a high end block polystyrene content, achieved with these end block molecular weights.

If the weight average molecular weights of each of the end blocks are less than about 15 000, g articles can be formed by dip forming, but their strengths are reduced and unacceptably low for some applications. Such articles have poor mechanical properties. Dip formed articles made using S-ED-S block copolymers having end block weights of less than about 15 000 tend to crack during drying and fusion, possibly due to their poor mechanical properties at elevated temperatures. On the other hand, when the weight average molecular weight of the polystyrene end blocks exceeds about 15 000Da, and is preferably in the 18 000 to 20 000Da range, the films exhibit superior strength properties and no crack formation during drying and fusion. In this case, it is desirable to have one styreneethylene/butylene-styrene block copolymer component with a total weight average molecular weight exceeding at least about 150 000Da. When the weight average molecular weight of the polystyrene end blocks exceeds about 24 000Da, the dispersion has good film-forming properties in dip forming, but the physical properties are not as good as those where the weight average molecular weight is in the 18 000 to 20 000 range.

The polystyrene end blocks typically constitute about 25-35wt% of the total molecule. The total molecular weight of the copolymer is typically from about 50 000 to about 300 000Da.

[l:DayibBCp30859.doc:mef The styrene-ethylene/butylene-styrene block copolymer may optionally have end-block compatible resins added to the polystyrene end blocks. The added end-block compatible resin increases the glass transition temperature (Tg) of the styrene-ethylene/butylene-styrene block copolymer. The increased Tg allows the final products to be used at higher temperatures than otherwise possible, as the product tends to become somewhat sticky at and above Tg. An example of such an end-block compatible resin is poly alpha methyl styrene.

The styrene-ethylene/butylene-styrene block copolymer is to be distinguished from other block copolymers that have sometimes been used in synthetic rubber compositions, such as styreneisoprene-styrene and styrene-polybutadiene-styrene block copolymers. It has been known to make thin rubberlike articles from S-I-S and S-B-S block copolymers, see for example, US 3 933 723. The use of these S-I-S and S-B-S block copolymers eliminates the need for vulcanisation of the articles, but the articles are subject to oxidation and ozone damage.

The use of an styrene-ethylene/butylene-styrene block copolymer, as distinct from other types, is critical to the success of the present invention, for two reasons. First, elastomers based upon the 15 styrene-ethylene/butylene-styrene block elastomeric triblock copolymers are resistant to attach by ozone, or by oxidative conditions, while S-I-S and S-B-S elastomers suffer from rapid cracking, when exposed to ozone, and cracking or hardening under oxidative conditions. Both of the latter copolymers are thus subject to failure even when protected by specific additives such as antiozonants or antioxidants which are deleterious in medical and other applications. The use of such special 20 additives is undesirable, as they may cause allergic reactions in some persons. The present elastomeric composition is hypoallergenic and may be contacted with the skin of the user for extended periods of time. Additionally, in spite of the special additives, scission cracking can lead to premature failure by ozone cracking of the articles made from S-I-S and S-B-S compositions, particularly when the articles are stored in a folded condition and then stretched before and during use.

Second, the mechanical properties of the styrene-ethylene/butylene-styrene triblock copolymers may be selected to provide the desirable combination of tensile strength, elasticity, and tactility that is required in some applications. styrene-ethylene/butylene-styrene elastomeric triblock copolymers have higher tensile strength, lower elastic elongation, and higher stress at 50-500% elongation than the S-I-S and S-B-S triblock elastomers.

The structure, properties, and some applications of some styrene-ethylene/butylene-styrene elastomers have been disclosed in US 3 485,787; 3 830 767; 4 006 116; 4 039 629; 4 041 103; 4 386 179; 4 481 323; 4 511 354; and 4 613 640.

The styrene-ethylene/butylene-styrene block copolymers are available commercially in a range of solution viscosity/copolymer concentration values. The solution viscosity/copolymer concentration value is determined by measuring the viscosity of a copolymer that has been previously dissolved in a solvent at a specified level. The solution viscosity/copolymer concentration value is a conventional approach for uniquely defining the nature of a block copolymer whose central and end block content has been specified by type and relative amount. For example, an styrene-ethylene/butylene-styrene block copolymer is uniquely specified by the stated composition of polystyrene end blocks and poly- (ethylene-butylene) central blocks, the relative amount of end blocks and central blocks, and the [:\DayLibLIBCp30859.doc:mef solution viscosity/copolymer concentration. Thus, a block copolymer is uniquely defined by stating that it is of the styrene-ethylene/butylene-styrene type, that the percentage of polystyrene end blocks is, for example, 28wt% of the total copolymer, and that the Brookfield Viscosity of a 20wt% solution in toluene at 25*C is 1500cp.

The commercially available styrene-ethylene/butylene-styrene block copolymers are manufactured in a precise manner so that each of the commercially available materials is closely controlled to meet such standards. Shell Kraton G1650 is an styrene-ethylene/butylene-styrene block copolymer having a styrene/central block ratio of 28/72 and a Brookfield Viscosity in toluene solution concentration) at 25*C of 1500. Shell Kraton G1651 is an styrene-ethylene/butylene-styrene block copolymer having a styrene/central block ratio of 33/67 and a Brookfield Viscosity in toluene solution (20wt% concentration) at 25"C of 2000. Shell Kraton G1652 is an styrene-ethylene/butylenestyrene block copolymer having a styrene/central block ratio of 29/71 and a Brookfield Viscosity in toluene solution (20wt% concentration) at 25 0 C of 550.

The styrene-ethylene/butylene-styrene block copolymer may comprise molecules with 15 substantially the same molecular weight. It may also comprise mixtures of molecules with two or more different molecular weights. The molecular weights and/or mixtures of molecular weights are selected to contribute to achieving desired mechanical properties in the final product. For example, in one preferred embodiment, mixtures of styrene-ethylene/butylene-styrene molecules as disclosed in US 5 112 900 and 5 407 715 are utilised in order to achieve the required mechanical properties to meet ASTM specifications. The present studies have demonstrated that styrene-ethylene/butylenestyrene polymer blend compositions in most cases exhibit superior film properties compared to typical single commercial polymers, although the formulations with a single commercial polymer are suitable for at least some applications. In particular, styrene-ethylene/butylene-styrene polymer blends with at least one polymer with a high weight average molecular weight such as Kraton G1651 tend to have performance superior to other styrene-ethylene/butylene-styrene blends.

An oil (also sometimes termed a "plasticiser") is provided, numeral 22. The oil is preferably a mineral oil, which is a refined petroleum paraffinic hydrocarbon oil described in Entries 6971 and 6972 of the Merck Index, Eighth Edition. The preferred mineral oil has a specific gravity of 0.87 at 25"C, a viscosity of 170cs at 25 0 C, and a Hirschler molecular weight of 492. The selected oil should not swell or solubilise the polystyrene end segments. Formulations with high levels of oil form more stable dispersions with less surfactant than other formulations.

The styrene-ethylene/butylene-styrene block copolymer is furnished by the manufacturer as a solid. To form a mixture from which a suitable dispersion may be prepared, a solvent (toluene or cyclohexane in the preferred approach) is provided, numeral 24. The styrene-ethylene/butylenestyrene block copolymers and the mineral oil plasticiser are mixed together and dissolved in a mutual solvent, preferably toluene or cyclohexane, numeral 26.

A dispersion medium is prepared from water, numeral 28, and a surfactant, numeral 30. The surfactant may be an anionic or cationic form, or a mixture of ionic and nonionic types. Suitable surfactants are disclosed in US 3 360,599; 3 305 917; and 5 120 765. The preferred surfactant is an anionic surfactant. Cationic surfactants are operable but less preferred, because cationic surfactants [:TDayUibLIBC]30859.doc:mef may be allergenic but most anionic surfactants are hypoallergenic. Although most of the surfactant and its residues are leached out and removed during the manufacturing operation, small amounts may remain and may cause an allergic reaction in the product user, if the surfactant is not hypoallergenic. The surfactant 30 is mixed with the water, numeral 32, in an amount of from about 1 to about 5vol%. The surfactant 30 may also be produced in situ by adding and reacting surfactantforming chemicals. For example, oleic acid added to the oil phase (the styrene-ethylene/butylenestyrene solution) and potassium hydroxide added to the water phase react to form the surfactant potassium oleate upon mixing.

Optionally, modifying additives such as thickeners, defoamers, or buffers may also be supplied and added to the aqueous dispersion medium, numeral 31.

The mixture 26 of styrene-ethylene/butylene-styrene, oil, and solvent is mixed together with the mixture 32 of water and surfactant, numeral 34. The mixing 34 is performed under high-speed, highshear-rate conditions using a mixer designed to produce dispersions. A preferred mixer is a rotor/stator mixer such as an X-series 410-X6 mixer available from Charles Ross Co or a 15 Microfluidiser M210 available from Microfluidics Co. Several high-shear mixing passes may be required to obtain the desired particle size.

After dispersing step 34, the solvent (toluene or cyclohexane in the preferred approach) is removed from the dispersion, numeral 36, a step often termed "stripping". Stripping may be accomplished by any operable approach, with heat/vacuum stripping and steam stripping preferred.

20 The solvent has the highest vapour pressure of any of the components and is therefore vaporised and drawn out of the dispersion. Additional may be added in step 36, or water may be removed by heating or other approach in a concentration step 37. Optionally, a biocide may be added in step 37 as well.

Equivalently to the procedure discussed in relation to steps 20-36, the components may be mixed and the dispersion formed in other orders and by other paths. In one approach, for example, the styrene-ethylene/butylene-styrene block copolymer, the solvent, and some of the water are mixed together under high-shear conditions to form a first dispersion, and the oil and additional water are mixed together under high-shear conditions to form a second dispersion. Modifiers may be dispersed into either of the dispersions. The solvent is stripped from the first dispersion. The stripped first dispersion and the second dispersion are thereafter mixed to form a third dispersion.

Figures 2A and 2B illustrate two possible types of dispersions produced by the present approach of steps 20-36, an (styrene-ethylene/butylene-styrene/oil)-in-(water/surfactant) aqueous dispersion (Figure 2A) and a (water/surfactant)-in(styrene-ethylene/butylene-styreneloil) aqueous dispersion (Figure 2B). The type of dispersion produced is responsive to the relative amounts of the mixture 26 and the mixture 32 that remain after the stripping step 36, as well as the type and amount of the surfactant (which alters the surface energies of the phases). If a relatively small amount of (styrene-ethylene/butylene-styrene/oil)-solvent mixture is present, as compared with the amount of (water/surfactant) mixture, the dispersion has a structure of discrete droplets 50 of (styreneethylenelbutylene-styrene/oil)-solvent mixture in a continuous (water/surfactant) phase 52, as depicted in Figure 2A. In the dispersion of figure 2A, the (styrene-ethylene/butylene-styrene/oil) i:\DayUibUIBC]30859.doc:mef particles 50 are generally spherical with an average size of no more than about 2.m. If the particles are significantly larger, they have a tendency to separate and the dispersion is not stable. If a relatively large amount of (styrene-ethylene/butylene-styrene/oil)-solvent mixture is present, as compared with the amount of (water/surfactant) mixture, the dispersion has a structure of discrete droplets 54 of (water/surfactant) phase in a continuous (styrene-ethylene/butylene-styrene/oil)-solvent mixture 56, as depicted in Figure 2B. (The water/surfactant phase is termed the "dispersion medium" herein, whether it forms the continuous phase or, during intermediate stages of the processing, the dispersed phase.) The (styrene-ethylenelbutylene-styrene/oil)-in-(water/suractant) aqueous dispersion of Figure 2A is useful for dip-forming operations. The (water/surfactant)-in-(styrene-ethylene/butylenestyrene/oil/solvent) aqueous dispersion (Figure 2B) is a transient system present only during the preparation of the aqueous dispersion used in dip-forming operations.

Both types of dispersions of Figures 2A and 2B may be present at different times (but not coexisting) during the course of the preparation of the dispersion in steps 20-34. For example, in a 15 preferred inverse-dispersion approach as described in US 2 872 427 and 3 867 321, and CA 876 153, the mixture 26 may be prepared with a relatively high content of solvent, so that the volume of the styrene-ethylene/butylene-styreneloillsolvent mixture 26 is large as compared with that of the water/surfactant mixture 32. The high-shear-rate mixing step 34 produces a dispersion of water/surfactant mixture in styrene-ethylene/butylene-styrene/oil/solvent. When, however, the solvent is vacuum stripped and optionally more water is added in step 36, the relative volume of the remaining (styrene-ethylene/butylene-styrene/oil) mixture is much less, so that the dispersion inverts, resulting in the (styrene-ethylene/butylene-styrene/oil)-in-(water/surfactant) aqueous dispersion of Figure 2A.

Thus, the point in the processing at which the nature of the dispersion is to be judged is after the stripping step 36, not at earlier stages of the process.

Any other operable method for producing a dispersion may be used as well. Examples of such approaches are disclosed in US 3 238 173, 3 503 917 and 5 120 765.

The dispersion prepared by the steps 20-36 is preferably used in a dip forming operation.

(Although, as discussed earlier, it may be used in other types of forming and applying techniques as well.) Dip-forming technology is generally known for other applications, and will be described only briefly here. A form is provided, numeral 38. Any operable form may be used, and examples of such forms of most interest to the inventor include a human hand form 60, Figure 3, and a cylinder form 62 with a closed end, Figure 4. The hand form 60 is used to make elastomeric gloves, and the cylinder form 62 is used to make male condoms.

Articles are prepared by first dipping the form into a volume of the dispersion, numeral 40, and thereafter evaporating the water drying) and fusing the film, and optionally leaching the film, numeral 42. The preferred drying temperature is in the range of about 30 0 C to about 100°C, most preferably from about 70 0 C to about 90°C. Fusing is typically accomplished by heating the article to a temperature above the softening point of the end blocks of the styrene-ethylene/butylene-styrene block copolymer for a period of time. For conventional styrene-ethylene/butylene-styrene block copolymers, the fusing treatment is preferably in the range of about 120°C to about 150°C, most P:DayLibLIBC130859.doc:mef preferably in the range of about 130"C to about 1400C, in all cases for no more than about minutes. The high temperatures aid in achieving good mechanical properties. The styreneethylene/butylene-styrene block copolymer is stable at these temperatures. These conditions also allow making articles on dip lines designed for natural rubber dipping. However, as discussed herein, the styrene-ethylene/butylene-styrene block copolymers may be modified to increase their glass transition temperatures, so that the fusing temperature will correspondingly be increased. The times and temperatures of the fusing treatment may be varied, with shorter times used for higher temperatures and longer times used for lower temperatures.

Optionally, the final article may be leached in warm water to remove any residual surfactants.

The preferred leach time is 10 minutes or less, preferably 5 minutes or less. Improved leach conditions of longer times and warmer temperatures provide improved film properties. The preferred leach temperatures are in the range of from about 30"C to about To prepare such an article, a sufficiently large amount of the dispersion is prepared in the manner described and placed into a dipping tank, at ambient temperature. A commercially available 15 form (typically made of aluminium, glass, plastic, or porcelain) in the shape of the desired article is coated with a release agent such as calcium carbonate slurry or calcium stearate. The form is "i thereafter dipped into the tank and removed slowly, leaving a thin, uniform layer of the aqueous dispersion deposited onto the form, much in the same manner that a layer of paint would be deposited upon the form if it were dipped into a container of paint. During dipping, the dispersion is distributed 20 evenly over the surface of the form by a combination of rotational and wavy motions applied to the form. The form and overlying layer of dispersion are dried in a stream of air to permit the water in the thin elastomeric layer to evaporate, at ambient or elevated temperature. Each dipped and dried layer is typically about 0.03-0.20mm thick. The dipping procedure is repeated as necessary to build up a completed layer of the required thickness. Thin articles prepared according to the dipping process of the invention have thicknesses of from about 0.03 to about 1.0mm, depending upon the thickness per layer and the number of layers. It is difficult to maintain the integrity of layers of less than about 9 0.03mm thickness. It is difficult to prepare articles more than about 1.0mm thick by dip forming. After drying and fusion of the film, the article is removed from the form, which is then reused. The article may be modified or treated in ways consistent with the present approach as, for example, by powdering the surface to allow it to be slipped onto the body. more easily, or provided with a compatible non-powder surface layer to permit easy donning.

There are several practical considerations in commercial dip forming of articles by the present approach. The solids levels in the dispersion into which the form is dipped is in the range of from about 30 to about 65wt%, most preferably from about 55 to about 63wt%. At about 55wt% solids, many dips are required to achieve desired glove thickness to meet ASTM specifications. At about to about 63wt% solids, 2-3 dips provide satisfactory films of 0.25 to 0.3mm thickness. Dipping conditions such as former temperature and extraction speed may be varied to achieve the desired thickness. A uniform film is achieved by rotation or wavy motion of the form. Thicker films may be made with lower solids content of the dispersion or by modifying the viscosity of the dispersion by adding thickeners. The preferred dip method does not use a coagulant on the form. Other dipping [:DayUibLIBC]30859.doc:mef processes may also be used. A bead may be formed easily when the film is hot, preferably after exiting the fusion oven.

The following examples illustrate the application and practice of the present invention. These examples are presented by way of illustration and not of limitation, and should not be interpreted as limiting of the invention in any respect.

Example 1 About 150g of a 16wt% toluene solution of 40 parts by weight Kraton G1650, 40 parts by weight Kraton G1651, and 10 parts by weight Kraton G1652 styrene-ethylene/butylene-styrene block copolymers, and containing 56phr oil, was dispersed in about 100g of water containing 1g of Emcol K- 8300 surfactant obtained from Witco Chemical. Dispersion was accomplished with a rotor/stator assembly under high shear conditions for two minutes. The solvent was stripped off in a rotovap under hear and vacuum, and the solution diluted by adding water. The dispersion was used in a dipforming operation to form an elastomer film.

Example 2 i 15 About 150g of a cyclohexane solution of 40 parts by weight Kraton G1650, 40 parts by weight Kraton G1651, and 10 parts by weight Kraton G1652 styrene-ethylene/butylene-styrene block copolymers, and containing 48phr oil, was dispersed in about 150g of water containing 0.67g of sulfosuccinate surfactant. Dispersion was accomplished with a rotor/stator assembly under high shear conditions for two minutes. The cyclohexane was stripped off and the dispersion concentrated 20 to obtain an aqueous dispersion of styrene-ethylene/butylene-styrene block copolymer and oil. The dispersion was used in a dip-forming operation to form an elastomer film, which was dried and fused at 80-95 0 C for 10-20 minutes. The resulting film exhibited excellent mechanical strength properties.

Example 3 A dispersion was made as in Example 1, except that the final dispersion contained Emcol K-8300 surfactant. The film produced in dip forming was fused at 80-95°C for 10-20 minutes.

The resulting film exhibited excellent mechanical strength properties.

Example 4 An styrene-ethylene/butylene-styrene polymer blend composition was prepared by dissolving 103.13g of Kraton G1651, 154.69g of Kraton G1650, and 154.69g of mineral oil in 2088g of toluene.

The weight average molecular weight of the polystyrene end blocks was estimated to be about 18 000Da. An aqueous dispersion was prepared using 600g of this solution and 466g of water containing 3.25g of Emcol K-8300 and 3.25g of potassium rosin soap. The dispersion was concentrated by vacuum and heat in a rotovap after stripping the toluene. The resulting aqueous dispersion had a solids content of about 54wt%.

Films were dip formed from this dispersion using warm glass condom formers, using multiple dips to obtain a thickness of 0.05-0.09mm. The film was dried at about 70-80*C after each dip. After the last dip, the film was heated at 130°C for 5 minutes and then leached in warm water for 5 minutes.

The film was then heated to 130 0 C for 25 minutes, cooled, and stripped from the form after application of powder. The condoms produced in this manner had a tensile strength of 22.37MPa, a modulus at 500% elongation of 2.69MPa, and an elongation at break of 812%.

I:\DayibLIBC30859.doc:mef Example An styrene-ethylene/butylene-styrene blend formulation was prepared as in Example 4, except that the blend contained 127.74g of Kraton G1651, 151,68g of Kraton G1650, 31.94g of Kraton G1652, and 175.64g of mineral oil. The weight average molecular weight of the polystyrene end blocks of the blend is estimated to be 17 800Da.

An aqueous dispersion was prepared as in Example 4, and dispersion concentrated to 63.23wt% solids. Condoms were prepared as in Example 4 in a thickness range of 0.1 to 0.16mm.

The films had a tensile strength of 23.78MPa, a modulus at 500% elongation of 2.94MPa, and an elongation at break of 839%.

Samples of the condoms were sterilised by gamma radiation at a dose of 29.9KGy to 39.1KGy.

These samples showed a tensile strength of 20.61MPa, a modulus at 500% elongation of 2.64MPa, and an elongation at break of 897%.

Example 6 An styrene-ethylene/butylene-styrene blend formulation was prepared as in Example 4, but I 15 containing 70phr of mineral oil. The weight average molecular weight of the polystyrene end blocks is estimated to be 18 000Da as in Example 4. Dispersions and films were prepared as in Example 4, using 600g of the blend solution and 466g of water containing 3.25g of Emcol K-8300 and 4g of DRS 42 surfactant obtained from Arizona Chemical Co. The dispersions were concentrated and condoms were dip formed from this dispersion at about 0.04 to about 0.06mm thickness. The films showed a tensile strength of 18.8MPa, a modulus at 500% elongation of 2MPa, and an elongation at break of 884%. The present dispersion-dipped condoms showed burst volumes and burst pressures similar to those of solution-dipped films. Gloves were dip formed using ceramic formers and the above dispersions.

~Example 7 An styrene-ethylene/butylene-styrene solution formulation was prepared by mixing 242.65g of Kraton G1652 and 169.9g of mineral oil in 2087.5g of toluene. A dispersion was prepared as in Example 4. The weight average molecular weight of the end blocks was estimated to be 7250Da.

Condoms dipped from this dispersion at 0.05 to 0.07mm thickness showed signs of cracking of the film during drying and fusion of the film. The tensile strength of the film was 4.36MPa and the modulus at 500% elongation was also about 4.36MPa.

Example 8 An styrene-ethylene/butylene-styrene solution blend was prepared using Kraton G1651 and Kraton G1652 with 70phr mineral oil in toluene. A dispersion was made as in Example 4. The weight average molecular weight of the polystyrene end blocks of the blend was estimated to be about 24 000D. The dispersion was concentrated to 63.5% solids, and condoms were dip formed from this dispersion. The dispersion had excellent film forming characteristics and moderate strength.

Example 9 An styrene-ethylene/butylene-styrene blend composition as detailed in Example 5 was prepared at about 21wt% solids. The dispersion was made using 3kg of the solution and 4kg of water containing 30g of Emcol K-8300 and 70g of potassium rosin soap in a Microfluidiser at 15.17MPa in 3 ::\DayibUIBCJ30859.doc:mef 11 passes. A predispersion was made before passing through the Microfluidiser. The dispersion had an average particle size of 0.47pn. The dispersion was stripped and concentrated. The dispersion showed good film-forming characteristics and good film strength properties.

Example An styrene-ethylene/butylene-styrene solution was prepared as in Example 5 and a dispersion made using the Ross X-Series mixer. The dispersion was concentrated to 61wt% solids. The dispersion showed good stability and good film formation as in Example The present approach provides a technique for forming good-quality films from an aqueous dispersion. The films have the advantageous properties as disclosed in US 5 112 900 and 5 407 715, but the dip-forming operation is more economical than the approach described in these patents.

Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

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Claims (6)

1. An elastomeric article comprising: a styrene-ethylene/butylene-styrene block copolymer, where the styrene-ethylene/butylene-styrene block copolymer has end blocks each having a weight average molecular weight of more than about 15 000Da; and an oil.

2. The article of claim 1, wherein the styrene-ethylene/butylene-styrene block copolymer comprises block copolymers of substantially the same molecular weight.

3. The article of claim 1, wherein the styrene-ethylene/butylene-styrene block copolymer comprises a mixture of at least two styrene-ethylene/butylene-styrene block copolymers of different molecular weights.

4. The article of any one of claims 1 to 3 1, wherein at least one of the styrene- ethylene/butylene-styrene block copolymer components has a total weight average molecular weight exceeding at least about 150 000Da.

An elastomeric article comprising: a styrene-ethylene/butylene-styrene block copolymer, said elastomeric article being substantially as hereinbefore described with reference to any one of the 15 examples.

6. An elastomeric article comprising: a styrene-ethylene/butylene-styrene block copolymer, said elastomeric article being substantially as hereinbefore described with reference to figure 3 or figure 4 of the accompanying drawings. DATED this fourth Day of August, 2000 Tactyl Technologies, Inc. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 6O S S 56a 0 *6 6 6 S 6@ [I:\DayLib\.IBC30859.doc:mef