SLIP CONTROL ARTICLE FOR WET AND DRY APPLICATIONS

Abstract: A slip control article including a backing layer (21, 52) having a first surface (24) with an array of at least 15,5 upstanding stems (26, 56) per square centimeter and a second surface (25). At least a portion of the upstanding stems is an elastomeric material and the stems have an aspect ratio of at least 1.25. The first surface has a static coefficient of friction when dry of at least 0.6 and a static coefficient of friction when wet within 20 % of the static coefficient of friction when dry. The first surface has a peel strength and a tensile strength of substantially zero when engaged with another slip control article. The first surface has a relatively high shear strength when engaged with another slip control article. The high shear forces are due primarily to the frictional properties of the elastomeric materials, not a mechanical interlock of the stems, such as on a mechanical fastener.

Description: SLIP CONTROL ARTICLE FOR WET AND DRY APPLICATIONS Field of the Invention The present invention is directed to a slip control article having a pleasant and soft feel, high friction properties, and good performance in wet and dry conditions. Background of the Invention The development of enhanced grip and anti-slip surfaces typically centers around the materials and the surface topology of the article. Common materials include natural and synthetic rubbers, styrenic block co-polymers, latex, ethylene vinyl acetate, ethylene-propylene rubber, polyurethane, polyester co-polymers, polyimides, and the like. The surface topology can range from smooth to having exaggerated gripping structures. U.S. Patent No. 3,585,101 discloses a thin sheet of a soft, ductile, flexible material, such as aluminum, brass, plastic or the like, having a knurled pattern embossed to provide an improved gripping surface. The sheet can be applied to solid objects using an adhesive. U.S. Patent No. 4,488,918 discloses a plastic film having a non-slip surface comprising spaced, random patterns of rigid peaks and ridges formed of a second thermoplastic material co-extruded with and bonded to a plastic film. The surface has a pattern of relatively high, sharp, irregular plastic peaks and ridges, sufficiently sharp, hard and rough to effect a mechanical gripping with other surfaces. U.S. Patent No. 5,234,740 discloses a slip control surface with a structured surface. The structured surface includes an array of protrusions, typically triangular pyramids. The patent discloses that the sheeting may be applied to the handles of athletic equipment such as softball bats, golf clubs, tennis, racquetball, squash, badminton racquets, as well as the handles of tools. Brief Summary of the Invention The present invention relates to an improved gripping surface that has a pleasant and soft feel, high frictional properties and good gripping performance in both wet and dry conditions. The gripping surface is a soft micro-structured surface having an array of flexible upstanding stems of a variety of shapes produced from a thermoplastic elastomer. The size, spatial distribution, flexibility of the stems, stem array pattern, and the properties of the elastomer material all contribute to the soft feel of the surface, vibration dampening, and the gripping performance under wet and dry conditions. The various embodiments of the present slip control surface may include micro-channels, an absorbent layer and hydrophilic/hydrophobic regions all for directing fluids away from the upstanding stems, leaving them dry and providing high frictional performance even in wet conditions. The present slip control article may be formed in a sheet structure, such as a wrap that can be applied to another article. Alternatively, the slip control article may be incorporated into a variety of molded or manufactured articles, including sport grips for golf clubs, baseball bats, racquets, bicycle handles, exercise equipment, household articles, construction and surgical tools, non-slip walking surfaces for swimming pool decks, diving boards, bathtubs. In one embodiment, the slip control article comprises a backing layer having a first surface with an array of at least 15.5 stems/centimeter 2 (100 stems per square inch), and more typically at least 54 stems/centimeter 2 (350 stems per square inch) and a second surface. At least a portion of an exterior surface of the upstanding stems is an elastomeric material. The stems have an aspect ratio (stem height: stem diameter) of at least 1.25, and preferably at least 1.5, and more preferably at least 2.0 and most preferably greater than 3.0. The first surface has a static coefficient of friction when dry of at least 0.6 and a static coefficient of friction when wet within 20% of the static coefficient of friction when dry. Therefore, frictional properties do not substantially degrade when water is present. The first surface has a peel strength and a tensile strength of substantially zero when engaged with another slip control surface. In one embodiment, an array of upstanding stems comprising an elastomeric material is also formed on the second surface. The second surface has a static coefficient of friction when dry of at least 0.6 and a static coefficient of friction when wet within 20% of the static coefficient of friction when dry. The second surface has a peel strength and a tensile strength of substantially zero when engaged with another slip control surface. In other embodiments, the static coefficient of friction when dry is at least 1.0 or at least 2.0. The first surface has a dynamic shear strength of at least 23,268 dynes/centimeter 2 (5 4 ounces/ inch 2 ), and preferably more than 43,090 dynes/centimeter 2 (10 ounces/ inch 2 ), and more preferably at least 77,562 dynes/centimeter 2 (18 ounces/ inch 2 ) and most preferably at least 107,725 dynes/centimeter 2 (25 ounces/ inch 2 ) when engaged with another slip control surface at a pressure of about 53 grams/6.45 centimeter 2 . The high shear forces are due primarily to the frictional properties of the elastomeric materials, not a mechanical interlock of the stems, such as on a mechanical fastener. The backing layer may be one or more layers, such as a reinforcing web, a foam layer, a substantially inelastic polymeric layer, or an adhesive or foamed adhesive layer, depending on the application of the slip control article. In one embodiment, the backing layer may be the elastomeric material integrally formed with the upstanding stems. The backing layer may be elastic or inelastic, thick or thin, porous or non-porous, with or without an adhesive layer, etc In one embodiment, a non-elastomeric backing layer may form a portion of the upstanding stems Since the backing layer may optionally be extremely thin, the present slip control article may configured as a very thin wrap or gripping tape suitable for use as lightweight gripping applications. Alternatively, the backing layer may be a portion of a molded, extruded or manufactured article Brief Description of the Several Views of the Drawing Figure 1 is a side-sectional view of a slip control article in accordance with the present invention Figure 1 A is a side-sectional view of a two-sided slip control article in accordance with the present invention Figure 2 is a side-sectional view of an alternate slip control article in accordance with the present invention Figure 3 is a side-sectional view of co-extruded slip control article in accordance with the present invention Figure 3 A is a side-sectional view of an alternate co-extruded slip control article in accordance with the present invention Figure 4 is a side-sectional view of a slip control article with an absorbent layer on the second surface in accordance with the present invention Figure 5 A is a side-sectional view of a slip control article including micro- channels and an absorbent material in accordance with the present invention. Figure 5B is a top view of the slip control article of Figure 5A. Figure 6 is a schematic illustration of a water droplet interacting with a slip control article in accordance with the present invention. Figure 7 is a schematic illustration of water being channeled away from the upstanding stems on a slip control article in accordance with the present invention. Figure 8 is a perspective view of an exemplary article incorporating the slip control article of the present invention. Figure 9 is a schematic illustration of an exemplary method of manufacturing the slip control article in accordance with the present invention. Detailed Description of the Invention Figure 1 is a side-sectional view of a slip control article 20 in accordance with the present invention. The article 20 includes a backing layer 21 having a first surface 24 with an array of upstanding stems 26. The stems may be arranged in a regular or an irregular array. Various patterns of stems may be used, such as hexagonal, diagonal, sinusoidal, etc. The upstanding stems 26 are constructed of an elastomeric material. The entire exterior surface of the upstanding stems 26 are an elastomeric material. In the embodiment of Figure 1, the backing layer 21 is integrally formed with the upstanding stems 26 of an elastomeric material. The combination of the backing layer 21 and the upstanding stems 26 is sometimes referred to as a ste web. Although the illustrated embodiments show the stems 26 as being generally cylindrical, the sides of the stems 26 typically have a slight taper 35 to facilitate removal from the mold. A variety of non- cylindrical shapes can also be utilized, such as truncated cones or pyramids, rectangles, hemispheres, squares, hexagon, octagon, gum drops, and the like. The present slip control article 20 requires primarily upstanding stems 26 constructed of an elastomeric material and a backing layer 21 to hold the structure together. The elastomeric properties of the backing layer 21, however, do not fulfill all requirements for some applications, such as when the slip control article 20 is used as a gripping wrap. Therefore, additional backing layers 22, 34, 36 are optionally applied to the second surface 25 to reinforce the backing layer 21 The additional backing layer 22 may serve to stabilize and reinforce the slip control article 20, to resist stretching and improving tear resistance, as well as a variety of other functions Adhesive layer 34 and release liner 36 are optionally provided for attaching the present slip control article 20 to another surface As used herein, backing layer refers to an assembly having one or more layers supporting the upstanding stems, although typically at most one of these layers is integrally formed with the upstanding stems The backing layer is typically about 0 05 millimeters to about 0 38 millimeters (0 002 inches to 0 015 inches) thick In some instances, the backing layer is sufficiently thick to bond a reinforcing web during extrusion, such as a sheet of fabric, to impart increased tear resistance and tensile strength The reinforcing web is particularly useful when the slip control article is attached to a flexible substrate via sewing The backing layer may be a foamed or a solid polymeric material In one embodiment, the backing layer may include a porous and/or absorbent layer, such as layers of fibrous material or fabric scrim which may be woven or nonwoven A porous material is useful for absorbing moisture and/or directing moisture away from the upstanding stems In one embodiment, the backing layer includes a substantially inelastic layer to prevent necking or stretching of the slip control article It is desirable for the backing layer to be sufficiently compatible with the elastomeric material to keep the slip control article together Suitable backing layer materials include thermoplastic polyurethanes, polyvinyl chlorides, polyamides, polyimides, polyolefins (e.g , polyethylene and polypropylene), polyesters (e g , polyethylene terephthalate), polystyrenes, nylons, acetals, block polymers (e g , polystyrene materials with elastomeric segments, available from Shell Chemical Company of Houston, Texas, under the designation KRATON™, polycarbonates, thermoplastic elastomers (e g polyolefin, polyester or nylon types) and copolymers and blends thereof The thermoplastic material may also contain additives, including but not limited to fillers, fibers, antistatic agents, lubricants, wetting agents, foaming agents, surfactants, pigments, dyes, coupling agents, plasticizers, suspending agents, hydrophilic/hydrophobic additives, and the like The optional adhesive layer typically comprises an adhesive selected to provide a bond to a substrate article to which the slip control surface is to be applied, such as pressure sensitive adhesives, thermosetting or thermoplastic adhesives, radiation cured adhesives, adhesives activated by solvents, and blends thereof. The adhesive may include filaments The backing layer can optionally be laminated or impregnated with the adhesive One adhesive useful in the present invention is Adhesive Transfer Tape 950 available from Minnesota Mining and Manufacturing Company Many suitable epoxy, urethane, synthetic or natural based rubber and acrylic adhesives are commercially available for this purpose as well. Depending upon the application, the adhesive may releasably bond or permanently bond the slip control article to a surface Figure 1 A is a sectional view of a two-sided slip control article 20' as generally illustrated in Figure 1, without the additional backing layers 22, 34, 36. The article 20' includes a backing layer 21 ' with an array of upstanding stems 26' on both the first and second surfaces 24', 25' The upstanding stems 26' are constructed of a single elastomeric material In the embodiment of Figure 1A, the backing layer 21' is integrally formed with the upstanding stems 26' of an elastomeric material In another embodiment, the upper and lower portions may be co-extruded from two different elastomeric materials A two-side slip control article in accordance with the present invention may be formed from the various disclosed embodiments Figure 2 is a side-sectional view of an alternate slip control article 40 in accordance with the present invention Backing layer 42 defines lower portions 44 of the stems 46 The upper portions 48 of the stems 46 are constructed of the elastomeric material The backing layer 42 and lower portions of the stems 44 may be constructed of a variety of materials, elastomeric or non-elastomeric, depending upon the application for the slip control article 40 At a minimum, the exterior surface of the upper portions 48 are an elastomeric material In one embodiment, the upper portions 48 of the stems 44 have hydrophobic properties Hydrophobic properties may be obtained by constructing the upper portions 48 from a hydrophobic material or treating the upper portions 48 to achieve hydrophobic properties For applications involving contact with non-polar liquids, the upper portions 48 of the stems 46 may be treated to achieve hydrophilic properties (e.g , corona treatment) Figure 3 is a side-sectional view of another alternate slip control article 50 formed by co-extrusion in accordance with the present invention The backing layer 52 protrudes into a center regions 54 to add structural integrity to the elastomeric stems 56 The backing layer 52 is typically a stiffer polymeric material Figure 3A is an alternate slip control article 50' formed by co-extrusion in accordance with the present invention The stems 56' and backing layer 52' are constructed of an elastomeric material The stems 56' protrude through a center region 54' of an additional backing layer 53' The additional backing layer 53' may provide structural stability, hydrophobic/hydrophilic properties or a variety of other functions. In on embodiment, the additional backing layer 53' may be an elastomeric material with properties different from those used to construct the stems 56' Figure 4 is a side-sectional view of an slip control article 70 incorporating a plurality of holes 72 through the backing layer 74 in fluid communication with an absorbent layer 76 The absorbent layer 76 draws moisture away from the elastomeric stems 78 to maintain good frictional properties in wet conditions Figures 5A and 5B illustrate a slip control article 80 incorporating micro- channels 82 on the backing layer 84 between the upstanding elastomeric stems 86 The micro-channels 82 utilize capillary forces to cause the rapid transport of a fluid in a direction of a driving force Absorbent layer 88 is located along the first surface 90 of the backing 84 to provide the driving force. Alternatively, the driving force may be gravity and/or hydrophilic areas on the stems 86 A number of mechanisms combine to give the present slip control article exceptional frictional properties in both wet and dry conditions Figure 6 is a schematic illustration of an individual water drop 60 residing on hydrophobic tips 62 of the stems 64 The drop 60 is easily removed from the stem 64 by shaking or gripping of the slip control article 66 The redistribution of water is also impacted by stem density Deposition of large amounts of water 60 results in distribution of the liquid at the base of the stems 64 while the tips 62 remain dry, as illustrated in Figure 7 When water or any other polar liquid is deposited on the surface of the slip control article 66, the tips 62 of the stems 64 remain exposed due to the hydrophobic nature of the thermoplastic elastomer polymer Constructing the backing layer from a hydrophilic material assists in directing the water 60 away from the tips 62 The upstanding stems 64 grip with other surfaces primarily due to the frictional properties of the elastomeric material of the stems. Frictional performance does not require the stems 64 to protrude into the other surface (i.e. mechanical engagement is not required). Therefore, frictional contact can be made with both soft and rigid materials. The present slip control article provides high shear forces when engaged with another slip control article, at minimal pressure. Since the upstanding stems are constructed substantially from a highly flexible elastomeric material, high shear forces are not derived from a mechanical interlock of the stems, such as on a mechanical fastener. Rather, the frictional properties of the upstanding stems are enhanced by the stem size, stem density, and stem pattern when two slip control articles are engaged with each other. Possible applications include gloves having the present slip control article located for gripping a surface also including the slip control article. Since the upstanding stems do not interlock, the present slip control article has substantially zero peel and tensile force when engaged with the same or a similar stem web structure. This feature is important to safe use of the present slip control article for gripping purposes, since the user must typically be free to quickly release the gripped item, without having to overcome any peel or tensile forces generated by the slip control articles. For example, the present slip control article can be wrapped around the handle bars of a bicycle and applied to bicycling gloves. When the user grips the handle bars of the bicycle, the two slip control articles engage to provide excellent slip control properties in shear with minimal pressure. However, the substantially zero peel and tensile forces allows the user to release the handle bars with substantially zero resistance from the two slip control articles. The soft feel of the present slip control article is due primarily to the nature of the elastomeric material and to ste geometry. The elastomeric material preferably has a Shore hardness of less than about 70D (Estane™ 58091); more preferably less than about 90A, and most preferably less than about 60A. The tensile modulus is preferably less than about 12 MPa, more preferably less than about 6 MPa, and most preferably less than about 4 MPa. Stem height, stem diameter, and spacing between the stems (referred to as stem geometry) are significant factors in establishing a soft feel on the surface. Generally, longer stems result in a softer feel due to their flexibility. As for stem spacing, the average distance between the tactile points in fingertips is approximately 1.27 millimeters (0.050 inches) When the spacing between the objects is less than half the tactile distance, it becomes difficult to distinguish between the protrusions on the surface Therefore, the best feel is typically obtained for a stem web with the highest available density of stem A stem density in excess of 310 stems/centimeter 2 (2,000 stems per square inch) creates a unique soft and pleasant feel for skin contact Referring again to Figure 1 , the stems need to be substantially upstanding to optimize the performance of the slip control article The stems are kept upstanding by the stem diameter and the nature of the elastomeric material The upstanding stems typically have a height 28 in the range of about 0 254 millimeters to about 1 27 millimeters (0 010 inches to about 0 050 inches), and more typically in the range of about 0 51 millimeters to about 1 02 millimeters (0 020 inches to 0 040 inches) The separation or gap 30 between adjacent stems 26 is generally in the range of about 0 254 millimeters and about 2 54 millimeters (0 01 inches to about 0 1 inches) and more typically in the range of about 0 46 millimeters to about 0 84 millimeters (0 018 inches to 0 033 inches) The stems 26 have a maximum cross sectional dimension 29 of about 0 076 millimeters to about 0 76 millimeters (0 003 inches to about 0 030 inches) The stems 26 are arranged on the backing in a density of at least 15 5 per centimeter squared (100 per square inch), and more typically about 54 per centimeter squared to about 1550 per centimeter squared (350 per square inch to about 10,000 per square inch) The stems have an aspect ratio of at least 1 25, and preferably at least 1 5, and more preferably at least 2 0 and most preferably greater than 3 0 , although aspect ratios in excess of 3 0 are possible for some applications Aspect ratio refers to the ratio of pin height to the maximum cross sectional dimension For pins with a circular cross section, the maximum cross sectional dimension is the pin diameter Figure 8 is a perspective view of an exemplary article 100 incorporating the slip control surface 102 in accordance with the present invention The article 100 is a molded grip having an opening 104 at one end, suitable for attachment to a variety of structures such as golf club, baseball bats, handles, and the like The article 100 may be made using a variety of processes, such as injection molding, profile extrusion, roll extrusion forming, etc Elastomeric Materials The elastomeric material can be any thermoplastic elastomer that can be heated to a state in which it can be flowed and molded, such as those described in G Holden et al , Thermoplastic Elastomers, (2 nd ed 1996) It is also within the scope of this invention to use two or more different thermoplastic elastomeric materials in either layered or blended form to define that portion of the slip control article The term "elastomer" or "elastomeric" is used to refer to rubbers or polymers that have resiliency properties similar to those of rubber In particular, the term elastomer reflects the property of the material that it can undergo a substantial elongation and then return to its original dimensions upon release of the stress elongating the elastomer In all cases an elastomer must be able to undergo at least 10% elongation (at a thickness of 0 5 mm), and more preferably at least 30% elongation, and return to at least 50% recovery after being held at that elongation for 2 seconds and after being allowed 1 minute relaxation time More typically, an elastomer can undergo 25% elongation without exceeding its elastic limit In some cases elastomers can undergo elongation to as much as 300% or more of their original dimensions without tearing or exceeding the elastic limit of the composition Elastomers are typically defined to reflect this elasticity as in ASTM Designation D883-96 as a macromolecular material that at room temperature returns rapidly to approximately its initial dimensions and shape after substantial deformation by a weak stress and release of the stress ASTM Designation D412-98 A can be an appropriate procedure for testing rubber properties in tension to evaluate elastomeric properties For some applications, thermoset elastomers may be used Generally, such compositions include relatively high molecular weight compounds which, upon curing, form an integrated network or structure The curing may be by a variety of methods, including chemical curing agents, catalysts, and/or irradiation The final physical properties of the material are a function of a variety of factors, most notably number and weight average polymer molecular weights; the melting or softening point of the reinforcing domains (hard segment) of the elastomer (which, for example, can be determined according to ASTM Designation D 1238-86), the percent by weight of the elastomer composition which comprises the hard segment domains, the structure of the toughening or soft segment (low Tg) portion of the elastomer composition; the cross-link density (average molecular weight between crosslinks), and the nature and levels of additives or adjuvants, etc Examples of classes of elastomers include anionic triblock copolymers, polyolefin-based thermoplastic elastomers, thermoplastic elastomers based on halogen- containing polyolefins, thermoplastic elastomers based on dynamically vulcanized elastomer-thermoplastic blends, thermoplastic polyether ester or polyester based elastomers, thermoplastic elastomers based on polyamides or polyimides, ionomeric thermoplastic elastomers, hydrogenated block copolymers in thermoplastic elastomer interpenetrating polymer networks, thermoplastic elastomers by carbocationic polymerization, polymer blends containing styrene/hydrogenated butadiene block copolymers, and polyacrylate-based thermoplastic elastomers Some specific examples of elastomers are natural rubber, butyl rubber, EPDM rubber, silicone rubber such as polydimethyl siloxane, polyisoprene, polybutadiene, polyurethane, ethylene/propylene/diene terpolymer elastomers, chloroprene rubber, styrene-butadiene copolymers (random or block), styrene-isoprene copolymers (random or block), acrylonitrile-butadiene copolymers, mixtures thereof and copolymers thereof. The block copolymers may be linear, radial or star configurations and may be diblock (AB) or triblock (ABA) copolymers or mixtures thereof Blends of these elastomers with each other or with modifying non-elastomers are also contemplated Commercially available elastomers include block polymers (e.g , polystyrene materials with elastomeric segments), available from Shell Chemical Company of Houston, Texas, under the designation KRATON™. Method of Manufacture The process illustrated in Figure 9 shows a three-roll vertical stack molding apparatus 150 which includes an extruder and extrusion die 152 adapted for extruding one or more layers of molten thermoplastic material 154 into a mold 156 In this case, the mold 156 is a roll 158, which has on its outer cylindrical surface a desired surface pattern for transference to the molten thermoplastic material 154 as it passes over the cylindrical surface of the roll 158 In the illustrated embodiment, the surface of the roll 158 has a plurality of arranged cavities 160 adapted to form a like plurality of upstanding stems 162 The cavities may be arranged, sized and shaped as required to form a suitable surface stem structures from the thermoplastic material 154 In one embodiment, a sufficient additional quantity of molten thermoplastic material 154 is extruded into the mold 156 to form a portion of the backing layer (see Figures 1 and 3) The roll 158 is rotatable and forms a nip 166, along with an opposed roll 168. The nip 166 between the roll 158 and opposed roll 168 assists in forcing the flow of molten thermoplastic material 154 into the cavities 160 and provides a uniform backing layer thereon The spacing of the gap forming the nip 166 can be adjusted to assist the formation of a predetermined thickness of the backing layer of thermoplastic material 154 Optionally, backing layer 164 is simultaneously brought into the nip 166. Depending upon the composition of the elastomeric material and the geometry of the upstanding stems 162, the backing layer 164 may be useful in efficiently remove the slip control article 172 from the mold 156 As illustrated in Figure 9, the slip control article 172 may traverse a third roll 170 after exiting the roll 158 In this process, the temperatures of all three rolls 158, 168, 170 may be selectively controlled to achieve desired cooling of the thermoplastic material 154. The third roll 170 also serves to define the further path traversed by the slip control article 172. The mold 158 may be of the type used for either continuous processing (such as a tape, a cylindrical drum or a belt), or batch processing (such as an injection mold or a compression mold) When making a mold 158 for forming the upstanding stems 162, the cavities 160 of the mold 158 may be formed in any suitable manner, such as by drilling, machining, laser drilling, water jet machining, casting, etching, die punching, diamond turning, engraving, knurling and the like The placement of the cavities determines the spacing and orientation of the slip control article The stems 162 typically have shapes corresponding to the shape of the cavities 160 The mold cavities can be open at the end of the cavity opposite the surface from which the molten thermoplastic material is applied to facilitate injection of the thermoplastic material into the cavity If the cavity is closed, a vacuum can be applied to the cavity so that the molten thermoplastic material fills substantially the entire cavity Alternatively, closed cavities can be longer than the lengths of the stem structures being formed so that the injected material can compress the air in the cavities. The mold cavities should be designed to facilitate release of the surface stem structures therefrom, and thus may include angled side walls, or a release coating (such as a Teflon material layer) on the cavity walls The mold surface may also include a release coating thereon to facilitate release of the thermoplastic material backing layer from the mold. In some embodiments, the cavities can be angled relative to the surface of the roll. The mold can be made from suitable materials that are rigid or flexible. The mold components can be made of metal, steel, ceramic, polymeric materials (including both thermosetting and thermoplastic polymers such as silicone rubber) or combinations thereof. The materials forming the mold must have sufficient integrity and durability to withstand the thermal energy associated with the particular flowable thermoplastic material used to form the backing layer and surface topographies In addition, the material forming the mold preferably allows the cavities to be formed by various methods, is inexpensive, has a long service life, consistently produces material of acceptable quality, and allows for variations in processing parameters The molten thermoplastic material is flowed into the mold cavity, and over the surface of the mold to form the layer of cover material To facilitate flow of the molten thermoplastic material, the thermoplastic material typically must be heated to an appropriate temperature, and then coated into the cavities. This coating technique can be any conventional technique, such as calendar coating, cast coating, curtain coating, die coating, extrusion, gravure coating, knife coating, spray coating or the like In Figure 9, a single extruder and extrusion die arrangement is shown However, the use of two (or more) extruders and associated dies allows simultaneous extrusion into the nip 166 of a plurality of thermoplastic materials to achieve a multi-component (layered or blended) laminate cover material The flow of the molten thermoplastic material 154 into the mold 158 may also be facilitated by the application of pressure between opposing rolls 168 When the backing layer 164 includes a porous material, the three-roll vertical molding apparatus 150 controls the degree of penetration of the molten thermoplastic material 154 In this fashion, the quantity of molten thermoplastic material 154 can be controlled to barely penetrate the surface coating of the backing layer 164, to penetrate the porous backing layer 164 on the opposite side of introduction of thermoplastic material 154 so as to almost encapsulate the backing layer 164. The penetration of the molten thermoplastic material 154 into the porous backing layer 164 may also be controlled by the temperature of the molten thermoplastic material 154, the quantity of thermoplastic material 154 in the nip 166, and/or by extruder flow rates in conjunction with the line speed of the mold cavities. After the molten thermoplastic material 154 has been coated into the mold cavities 160 and over the mold surface 156, the thermoplastic material is cooled to solidify and form the desired exterior surface topography thereon (e.g., upstanding stems 162). The solidified thermoplastic material is then separated from the mold 158. The thermoplastic material 154 will often shrink when it is solidified, which facilitates release of the material (e.g., surface stem structures and backing layer) and integral film layer from the mold (see Figure 1). Part or all of the mold may be cooled to aid in solidifying the surface stem structures and backing layer. Cooling can be effected by the use of water, forced air, heat transfer liquids or other cooling processes. Some molding processes, such as injection molding, may utilize thermoset elastomeric polymers. When thermosetting resins are used as the molten material, the resin is applied to the mold as a liquid in an uncured or unpolymerized state. After the resin has been coated onto the mold, it is polymerized or cured until the resin is solid. Generally, the polymerization process involves either a setting time, or exposure to an energy source, or both, to facilitate the polymerization. The energy source, if provided, can be heat or radiation energy such as an electron beam, ultraviolet light or visible light. After the resin is solidified, it is removed from the mold. In some instances, it may be desired to further polymerize or cure the thermosetting resin after the surface stem structures are removed from the mold. Examples of suitable thermosetting resins include melamine, formaldehyde resins, acrylate resins, epoxy resins, urethane resins and the like. The formation of a backing layer having upstanding stem structures on at least one side thereof can be performed by injection molding or profile extrusion, such as is disclosed in U.S. Patent Nos. 4,290, 174 (Kalleberg); 5,077,870 (Melbye et al.); and 5,201, 101 (Rouser et al.). Test Procedure For Measuring Static and Dynamic Coefficients Of Friction The static and dynamic coefficient of friction for each film sample was measured on a Thwing- Albert Model 225-1 Friction/Peel Tester available from Thwing- Albert Instrument Company, Philadelphia, Pennsylvania. Equipment operation is specified in the Thwing- Albert Instruction Manual, Friction/Peel Tester, Model #225-1 revised 5/94, Software version 2 4 This analysis for the static coefficient of friction measured the horizontal force required to cause movement of a weighted 5 08 cm by 5 08 cm (2 inch by 2 inch) sample of the slip control article against a sample of artificial leather sold under the name Ultrasuede™ HP available from Toray Ultrasuede America located in Manhattan, NY The friction test specimen were prepared by anchoring a 5 08 cm by 5 08 cm (2 inch by 2 inch) sample of the slip control article to a 5 08 cm by 5 08 cm (2 inch by 2 inch) metal test sled The test specimen were attached to the sled with a two sided pressure sensitive adhesive such as SCOTCH 9851, available from Minnesota Mining and Manufacturing Company, St Paul, Minnesota The metal test sled weighed 500 grams. An additional weight of 500 grams was applied to the top of the block making the total weight 1000 grams To prepare the artificial leather sample for the friction test a sample approximately 10 16 cm by 30 48 cm (4 inches by 12 inches) was anchored to a metal sheet with a two sided pressure sensitive adhesive tape, such as SCOTCH 9851 to prevent movement and wrinkling of the sample during the test The metal sheet with the sample adhered was clamped on to the metal platen testing surface with the provided spring clip The metal test sled with film sample on bottom of the sled and additional weight weighing 1000 grams in total was placed on the fabric and pulled for 10 seconds at a speed of 5 1 cm (2 inches) per minute across the fabric per instructions specified in the instructions manual The static coefficient of friction was then calculated by the machine wherein the measured horizontal force to cause slippage on the sample was divided by the 1000 gram normal force of the sled At least five measurements were recorded for each friction test sample and slip control article. Arithmetic averages were calculated by the friction/peel tester Test Method For Dynamic Shear Strength The dynamic shear strength was measured on an I-mass peel tester The tester was set up in the 180° Peel Mode A sample about 3 8 cm x 12 7 cm (1 5 inches x 5 inches) of stem web was attached using a double sided tape, such as 3M 404, and centered lengthwise to about 1 6 mm (1/16 inch) thick, 6 35 cm x 22 9 cm (2 5 inches wide x 9 inches long) aluminum test panel Similarly, a sample about 2.54 cm x 2 54 cm (1 inch x 1 inch) of stem web was attached to the center of about 1 6 mm (1/16 inch) thick, 6 35 cm x 22 9 cm (2 5 inches wide x 9 inches long) aluminum test panel The panels were then placed together with the stems of each sample in contact with each other The engaged thickness of the two samples without any pressure applied including the aluminum panels was measure using a digital caliper gauge The weight of the upper panel was approximately 53 grams An aluminum panel with the larger sample of stem web was attached to the moving platform of the I-mass tester with the stem web side up The aluminum panel with the sample about 2 54 cm x 2 54 cm (1 inch x 1 inch) of stem web was placed on top so that the stem web were in an engaged position The stem web was positioned so that it was at the end farthest away from the force gauge so that the sample on the upper panel would be pulled through the lower sample A bar was placed over the engaged pair with a gap approximately 0 13 mm - 0 254 mm (0 005 - 0 010 inches) greater than the engaged thickness This bar is designed to prevent the samples from disengaging without exerting undue pressure to engage the two stem web samples The end of the upper aluminum panel was attached to the force gauge in a position so that the gauge would measure a force directly parallel to the moving platform The 1-mass tester was balanced, zeroed and adjusted to measure a 2 second averaging time The position of the spacing bar was adjusted so that it would be directly above the stem web sample during the 2 second averaging time The platform rate was set at 30 5 cm/minute (12 inches/minute) The peak, valley, and average forces were measure for each sample Each sample was tested three times and the average values were calculated Materials Used in the Examples A variety of elastomeric materials were used in the preparation of the samples of the examples These materials are summarized in Table 1 Some properties of some of the samples are summarized in Table 2 Table 1 Table 2 Rheology and Morphology of the blends Viscosities of both Estate™ 58661 and Vector™ 411 1 were measured over several decades of shear rate using both a DSR and a capillary rheometer (CR) at 204 °C (400 °F), the temperature used in the stem web extrusion It is apparent that at higher shear rates (> 10 s-1), the viscosity and elasticity modulus of Vector™ 41 1 1 are approximately twice that of Estane™ 58661 Scanning electron microscopy (SEM) was used to investigate the morphology of blends of various compositions The blends were mixed using a Brabender mixer and pressed into a silicone mold using a hot press method at about 216 °C (420 °F) at 6 9 MPa (1000 psi) for 60 seconds The tool containing the material was cooled on dry ice The sample was peeled from the mold Only hot-pressed blends, described below, were studied Micrographs were taken near the sample surface A dispersed morphology was present in nearly every sample Only in the 60/40 Estane™ 58661/Vector™ 4111 sample were any co-continuous structures present Examples Example 1 A 50 50 by weight of polyurethane resin Estane™ 58661 and a styrenic triblock copolymer Vector™ 4111 was dry blended as pellets Polyurethane provided durability and resiliency of the structure while Vector improved frictional performance The Estane™ 58661 was dried at about 82 3 °C (180 °F) for at least 4 hours The mixture of pellets was mixed with about 2 wt % of carbon black/polyurethane blend The content of carbon black in the final blend did not exceed 1 wt % The mixture was extruded as generally illustrated in Figure 9, except that the tooling was configured as a belt rather than a roll The extruder as a Davis Standard single screw extruder with about 6 35 cm (2 5 inches) screw diameter designed for polyolefin processing At about 8 revolutions per minute (rpm), the melt was discharged through the die at melt pressure of about 13 8 MPa (2000 psi) The temperature in the last zone of the extruder was about 216 °C (420 °F) The temperature of the die was about 232 °C (450 °F) The opening of the die lip was about 0 51 millimeters (0 020 inches) The melt was pressed into a silicone belt/tool with a metal roll at a nip pressure of about 345,705 Pa (50 psi) One of the rolls had a tooled surface that was heated to about 65 6 °C (150 °F) The surface contained an array of holes about 0 254 mm (0.010 inches) in diameter and about 0 46 cm (0 018 inches) apart A backing layer of double coated tape available from Minnesota Mining and Manufacturing Company under product designation 404 was introduced into the nip and bonded to the side of the web opposite the upstanding stems The web and double coated tape was removed from the tooled surface at a speed of about 1 5 meters/minute (5 feet per minute) The resulting stem web had about 490/centιmeters 2 (3159 stems per square inch) The center-to-center spacing of the stems was about 0 439 mm (0 0173 inches) in the x-direction and about 0 465 mm (0 0183 inches) in the y-direction Stem diameter was about 0 15 mm (0 0059 inches) and the stem height was about 0 625 mm (0 0246 inches) The gap between adjacent stems was about 0 127 mm (0 005 inches) Wetting capability of water was estimated by measuring a contact angle between a drop of water and flat substrate with the same composition as the stem web The contact angle was measured to be about 65°, which was expected for a hydrophobic material (see generally Figure 6) A large amount of water was then applied to the structured surface of the stem web and viewed in optical microscope Water completely filled the space between the stems The tips of the stems were exposed due to hydrophobic nature of the elastomer, as shown in Figure 7 As a result of the exposed tips, frictional properties were impioved when compaied to flat sheet performance, when tested under the same conditions The gripping performance was evaluated using two approaches The first set of experiments included direct measurements of the frictional properties of the stem web The results were compared to the performance of the flat substrate made of the same polymer blend as the stem web The second approach involved direct application of the stem web to an article A 68 6 cm x 2 54 cm (27 inches x 1 inch) strip of the web was wrapped around a golf shaft and compared to the existing golf grips performance in both wet and dry conditions A panel of evaluators took a series of swings with the golf club with the new grip The performance of the invention was believed to be superior to the control sample in wet conditions A similar test was conducted with a tennis racket Example 2 For more consistent removal of the stem web from the tooled surface and uniform application the articles, a two-layer construction was created using a co-extrusion process The tooling and processing parameters were as described in Example 1 unless otherwise specified Rather than the backing layer of the double coated tape in Example 1, a backing layer made of a 80 20 wt % blend of polyurethane Estane™ 58137 and Vector™ 41 1 1 was co-extruded with the stem web The polyurethane had hardness of 70 Durometer and the modulus of about 22 MPa (3200 psi) The stiffer backing layer was extruded using about 6 35 cm (2 5 inches) diameter screw at about 5 rpm The top layer which formed the stemmed portion of the construction was extruded using about a 3.2 cm (1 25 inches) diameter screw extruder operating at about 15 rpm The temperature profile was the same as described in Example 1 The polymer melt was discharged at a minimum pressure of about 6 9 MPa (1000 psi) and at the temperature in the front zone of about 216 °C (420 °F) Both melts were combined in Cloeren feed block model no 86-120-398 at about 232 °C (450 °F) A Cloeren extrusion die with a deckle system, model no 89-12939, was used The construction was removed from the tooled surface at about 1 5 meters/minute and about 3 meters/minute (5 fpm and 10 fpm) The resulting thickness of the each layer (not including the stems), at about 5 fpm take-up speed was about 0 254 mm (0 010 inches) Example 3 A stem web was made generally according to Example 2 using a tool with different stem geometry and a pressure of about 68,941 Pa (10 psi), resulting in shorter stems The stem web was a 80 20 by weight of polyurethane resin Estane™ 58661 and a styrenic triblock copolymer Vector™ 41 1 1 The backing layer was made of a 80 20 wt % blend of polyurethane Estane™ 58137 and Vector™ 41 1 1, co-extruded with the stem web as in Example 2 The resulting stem web had about 235/centimeters 2 (1516 stems per square inch) The center-to-center spacing of the stems was about 0 676 mm (0 0266 inches) in the x-direction and about 0 630 mm (0 0248 inches) in the y-direction Stem diameter was about 0 198 mm (0 0078 inches) and the stem height was about 0 307 mm (0.0121 inches). The gap between adjacent stems was about 0 127 mm (0.005 inches) Example 4 A stem web with a single layer construction and a density of about 139 stems/cm 2 (900 stems/square inch) was created using a tool with different stem geometry and the same processing conditions and polymer blend formulation as in Example 1 The stems had about 50% larger diameter than the stems on the about 465 stems/cm 2 (3000 stems /square inch) construction of Example 1, which lead to better durability of the construction Stem height was about 0 56 mm to about 0 61 mm (0 022 inches to 0 024 inches) At a distance between the pins of about 0 84 mm (0 033 inches), individual pins could be felt Thicker pins are also less flexible, which also contributed to a more rough, or coarse feel of the surface This surface is most suited for non-skin contact applications Example 5 A stem web was made using a tool with different stem geometry and substantially according to Example 1 with a 80 20 by weight of polyurethane resin Estane™ 58661 and a styrenic triblock copolymer Vector™ 41 1 1 The resulting stem web had about 46/centimeters 2 (299 ste s per square inch) The center-to-center spacing of the stems was about 1 68 mm (0 066 inches) in the x-direction and about 1 29 mm (0 0507 inches) in the y-direction Stem diameter was about 0 459 mm (0 0195 inches) and the stem height was about 0 617 mm (0 0243 inches) The gap between adjacent stems was about 0.254 mm (0 010 inches) The higher percentage of polyurethane increased durability of the resulting slip control article Example 6 Stem web sheets were made using silicone tooling similar to Example 1 and the hot press method discussed above The formulations are set forth in Table 3, where the ratios refer to percentage of Estane™ 58661 to Vector™ 411 1 The resulting stem web had about 490/centimeters 2 (3159 stems per square inch) The center-to-center spacing of the stems was about 0 439 mm (0 0173 inches) in the x-direction and about 0 465 mm (0 0183 inches) in the y-direction Stem diameter was about 0 15 mm (0 0059 inches) and the stem height was about 0 625 mm (0 0246 inches) The gap between adjacent stems was about 0 127 mm (0 005 inches) In order to quantitatively compare the group properties of various blend compositions in both wet and dry conditions, a Thwing-Alber friction/peel tester was used to measure both static (SFC) and dynamic (DFC) friction In addition, friction coefficients for flat sheets, i e the other side of the stem web, were also measured for a few of the blend compositions The average SFC and DFC values for stem webs prepared in a batch process using a heated press of various formulations are given in Table 3 Table 3 Frictional properties of blended stem webs in dry and wet conditions Stem samples made from pure Vector™ 4111 have the highest DFC and SFC, and pure Estane™ 58661 stem samples have the lowest DFC and SFC Mixtures are somewhere in between with a nearly linear relationship In addition, SFC and DFC for each blend decreases with the addition of water between the stems and the Ultrasuede™ substrate In fact, the addition of water causes an only about a 7% decrease in stem web friction for every blend composition Small differences in friction performance are found for 50/50 and 60/40 blends Based on frictional performance, the 60/40 formulations will lead to better wear properties since it possess a larger volume fraction of polyurethane Example 7 A stem web of 50 50 by weight of polyurethane resin Estane™ 58661 and a styrenic triblock copolymer Vector™ 41 1 1 was made according to Example 1 The stem geometry is as set forth in Example 1 A flat sheet was also made using this formulation The average SFC and DFC values for stem web and the flat sheet are given in Table 4 Table 4 Stem web and flat film comparison From Table 4 it is evident that both static and dynamic coefficients of friction are comparable for the stem web (60% Estane™ 58661 and 40% Vector™ 41 11) and flat sheet when measured in dry conditions However, when some water was added to the stem web, coefficient of friction of the flat sheet decreased by 30%, while stem web maintained its high friction, within the experimental error This result is consistent with the mechanism of wetting described on Figures 6 and 7 Example 8 Three samples of the stem webs of Examples 1, 3 and 5 were examined for dynamic shear strength using the test method described above A summary of the results is found in Table 5 Table 5 - Dynamic Shear Strength - Dynes/cm (ounces/inch ) The stem webs made according to Examples 1 and 5 had the best dynamic shear strength The samples from Examples 1 and 3 were more similar in stem density and stem diameter than those of Example 5 However, the stem height of the samples of Example 3 was approximately half the height of the stems of Examples 1 and 5 Even the relatively low density stem web of Example 5 outperformed the samples of Example 3 Therefore, stem height appears to be a significant factor in dynamic shear strength

Claims: What is claimed is 1 A slip control article for wet and dry conditions, comprising a backing layer having a first surface with an array of at least 15 5 upstanding stems per square centimeter (100 per square inch) and a second surface, at least a portion of the upstanding stems comprises an elastomeric material and the stems have an aspect ratio of at least 1 25, the first surface having a static coefficient of friction when dry of at least 0 6 and a static coefficient of friction when wet within 20% of the static coefficient of friction when dry, the first surface having a peel strength and a tensile strength of substantially zero when engaged with another slip control article 2 The article of claim 1 wherein the first surface has a dynamic shear strength of at least 77562 dynes/centimeter 2 when engaged with a first surface of another slip control article 3 The article of claim 1 wherein the backing layer comprises an elastomeric material integrally formed with the upstanding stems 4 The article of claim 1 wherein the backing layer comprises additional layers of at least one of a reinforcing web, a foam layer, a substantially inelastic polymeric layer, or an adhesive layer 5 The article of claim 1 wherein the backing layer comprises a blend of polyurethane and a polystyrene material with elastomeric segments 6 The article of claim 1 wherein the backing layer comprises a compound selected from the group consisting of elastomeric materials, polyvinyl, polyurethane, polyester, polyacrylic, polycarbonate, and polyolefin 7 The article of claim 1 further comprising an array of upstanding stems of an elastomeric material located on the second surface of the backing layer 8. The article of claim 1 wherein the elastomeric material comprise an elastic block copolymer, styrene isoprene styrene, styrene butadiene styrene, styrene ethylene butadiene styrene, or a blend thereof. 9. The article of claim 1 further comprising micro-channels on at least the first surface. 10. The article of claim 9 further comprising an absorbent material in fluid communication with the micro-channels. 11. The article of claim 1 wherein the backing layer includes holes between at least two of the upstanding stems. 12. The article of claim 1 wherein at least a portion of the upstanding stems comprise one of hydrophobic or hydrophilic properties. 13. The article of claim 1 wherein the upstanding stems have a height of about 0.254 mm to about 1.27 mm. 14. The article of claim 1 wherein the upstanding stems have a maximum cross sectional dimension of about 0.076 mm to about 0.76 mm. 15. The article of claim 1 wherein the elongation at yield of the elastomeric material is at least about 30%.

Inventors: KOBE JAMES J, LEVITT LEON, KOBE, JAMES, J., LEVITT, LEON
Applicants: 3M INNOVATIVE PROPERTIES CO, 3M INNOVATIVE PROPERTIES COMPANY
Application year: 1999
Main classification: B32B27
IPC codes: A63B49, A63B53, A63B59, B25G1, B32B25, B32B27, B62K21