Wear-Resistant Composites

Abstract

The composite structure combines a strong, hard, low friction film with a soft underlying layer to provide good overall wear resistance. In one aspect, the composite structure may be formed from an elastomeric material with optical properties suitable for retrographic detection. However, the resulting composite may also or instead be advantageously utilized in a variety of applications such as gaskets, seals, clamps, robotic end effectors, and the like that benefit from a compliant, wear-resistant contact surface.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 228279, filed August 21, 2021, the entire contents of which are incorporated herein by reference.

[0002] Technical Field The present disclosure relates generally to wear-resistant composite structures.

[0003] background It is often desirable to use soft elastomeric pads to contact objects. For example, a robotic finger may have soft pads on its fingertips for grasping objects. Similarly, a retrographic sensor uses a transparent elastomer with a reflective coating to capture three-dimensional surface data from an object that comes into contact with the sensor. After numerous repeated uses, such devices may wear out due to contact with rough objects or surrounding dirt or grit, eventually becoming unusable and requiring replacement. There remains a need for contact pads that can withstand wear during repeated use, for example, as contact pads for retrographic sensors or robotic systems.

[0004] overview The composite structure combines a strong, hard, low friction film with a soft underlying layer to provide good overall wear resistance. In one aspect, the composite structure may be formed from an elastomeric material with optical properties suitable for retrographic detection. However, the resulting composite may also or instead be advantageously utilized in a variety of applications such as gaskets, seals, clamps, robotic end effectors, and the like that benefit from a compliant, wear-resistant contact surface.

[0005] In one aspect, a device for abrasion-resistant contact with a target surface disclosed herein may include a support structure; a substrate disposed on the support structure, the substrate having a first Shore A hardness of 10 or less and a first thickness of at least 1 mm; and a thin film disposed on the substrate for contact with the target surface. The thin film may include a second Shore A hardness of at least 70, a second thickness not exceeding 200 μm, a tensile strength of at least 30 MPa, an elongation at break of at least 650%, and a dynamic coefficient of friction against brushed steel not exceeding 1.5. The thin film may include a thermoplastic polyurethane, a thermoset polyurethane, or a nitrile rubber.

[0006] In one aspect, a device for abrasion-resistant contact with a target surface disclosed herein may include a support structure; a substrate disposed on the support structure, the substrate having a first Shore A hardness of 10 or less and a first thickness of at least 1 mm; and a thin film disposed on the substrate for contact with the target surface. The thin film may include a second Shore A hardness of at least 50, a second thickness not exceeding 500 μm, a tensile strength of at least 10 MPa, an elongation at break of at least 300%, and a dynamic coefficient of friction against brushed steel not exceeding 1.5. The thin film may include a thermoplastic polyurethane, a thermoset polyurethane, or a nitrile rubber.

[0007] In one embodiment, a device disclosed herein may include a substrate comprising a first elastomer having a first hardness; and a thin film comprising a second elastomer covering a first surface of the first elastomeric substrate. The second elastomer may comprise: (a) a second hardness greater than the first hardness of the first elastomer, (b) high strength, and (c) a low coefficient of friction on a second surface facing away from the first surface of the first elastomeric substrate.

[0008] Implementations may include one or more of the following features: The high strength of the second elastomer may include a tensile strength greater than the first elastomer. The high strength of the second elastomer may include a tear strength greater than the first elastomer. The first elastomer and the second elastomer may be configured to provide a wear-resistant elastomeric pad. The first elastomer may have a Shore A hardness not greater than 20. The first elastomer may have a Shore A hardness not greater than 5. The second elastomer may have a Shore A hardness of at least 30. The second elastomer may have a Shore A hardness of at least 50. The thin film may have a thickness of 5 μm to 1000 μm. The thin film may have a thickness of 20 μm to 400 μm. The thin film may have a thickness of not greater than 500 μm. The thin film may have a thickness of not greater than 200 μm. The first elastomeric substrate may have a thickness greater than 500 μm. The first elastomeric substrate may have a thickness of at least 1 mm. The second elastomer may have a tensile strength of at least 10 MPa. The second elastomer may have a tear strength of at least 20 kN / m. The second elastomer may have a tensile strength of at least 30 MPa. The second elastomer may have an elongation at break of at least 300%. The second elastomer may have an elongation at break of at least 800%. The first elastomer may include at least one of polydimethylsiloxane, polyurethane, and a thermoplastic elastomer. The second elastomer may include polyurethane. The second elastomer may include thermoplastic polyurethane. The second elastomer may include nitrile rubber. The first elastomer may be optically transparent. The device may further include a rigid, optically transparent support structure for the first elastomer.The rigid, optically transparent support structure may be formed from at least one of quartz, acrylic, glass, polystyrene, epoxy, polycarbonate, polyurethane, polyethylene terephthalate (PET), glycol modified polyethylene terephthalate (PET-G), and polyvinyl chloride (PVC). The device may further include a homogeneous opaque layer between the first elastomer and the second elastomer. The device may further include an illumination system arranged to illuminate the first elastomer and an imaging system configured to capture an image of the homogeneous opaque layer through the first elastomer. The device may further include a flexible support structure for the first elastomer. The device may further include a robotic finger, the first elastomer and the second elastomer forming a contact pad for the robotic finger. The device may further include a rod passing through the opening, the first elastomer and the second elastomer forming an annular fluid seal for the rod in the opening. The thin film may include a low friction coating. The thin film may include an opaque layer. The device may further include an adhesive layer between the first elastomeric substrate and the thin film comprising a second elastomer. The first hardness of the first elastomer may not exceed a Shore A hardness of 5, and the first elastomeric substrate has a thickness of at least 1 mm between the thin film and the support structure. The thin film may have a thickness not exceeding 500 μm, and the second elastomer has a Shore A hardness of at least 50, a tensile strength of at least 10 MPa, an elongation at break of at least 300%, and a dynamic coefficient of friction against a brushed steel surface not exceeding 1.5. The first elastomer may not exceed a first Shore A hardness of 5, and the second elastomer has a second Shore A hardness of at least 70, an elongation at break of at least 850%, and a tensile strength of at least 30 MPa. The thin film may have a thickness of 10 μm to 500 μm. The thin film may have a thickness of 30 μm or more and 200 μm or less.The thin film may have a thickness of 50 μm or more and 100 μm or less.The second hardness of the second elastomer may be a second Shore A hardness at least 10 times greater than the first Shore A hardness of the first elastomer. The second surface of the thin film may provide a contact surface having a composite abrasion resistance greater than the abrasion resistance of the first elastomer alone or the second elastomer alone. The composite abrasion resistance may be at least 50% greater than the first elastomer alone or the second elastomer alone. The composite abrasion resistance may be at least 100% greater than the first elastomer alone or the second elastomer alone. The composite abrasion resistance may be at least 200% greater than the first elastomer alone or the second elastomer alone. The composite abrasion resistance and the abrasion resistance of the first elastomer and the second elastomer may be measured as the time to break (tear) under a 20 gram load against a belt sander with 200 grit sandpaper operating at 1900 feet (579.12 m) per minute. The abrasion resistance of the composite, and the abrasion resistance of the first elastomer and the second elastomer may be measured according to a standardized abrasion test.

[0009] In one aspect, a method disclosed herein may include providing a support structure; disposing a substrate on the support structure, the substrate comprising a first elastomer having a first hardness; and disposing a thin film of a second elastomer on a first surface of the first elastomeric substrate, the second elastomer having a second hardness greater than the first hardness of the first elastomer, the second elastomer having a low coefficient of friction on a second surface facing away from the first surface of the first elastomeric substrate, and the second elastomer having high strength and high elasticity.

[0010] Embodiments of the devices, systems, and methods described herein are illustrated in the following drawings, which are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the present disclosure. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows a cross-sectional view of a wear-resistant composite structure.

[0012] [Diagram 2] FIG. 1 illustrates the wear resistance of a composite material structure.

[0013] [Diagram 3] 1 is a cross-sectional view of a system including a wear-resistant composite structure.

[0014] [Figure 4] FIG. 2 illustrates the operating principle of a wear-resistant contact pad.

[0015] [Diagram 5] FIG. 2 illustrates the operating principle of a wear-resistant contact pad.

[0016] [Figure 6] FIG. 2 illustrates the operating principle of a wear-resistant contact pad.

[0017] [Figure 7] FIG. 2 illustrates the operating principle of a wear-resistant contact pad.

[0018] [Figure 8] FIG. 2 illustrates the operating principle of a wear-resistant contact pad.

[0019] [Figure 9] FIG. 13 shows the wear rate of various composites as a function of the experimental elastic limit for thin coated films.

[0020] Detailed Description All documents mentioned herein are incorporated by reference in their entirety. Reference to a singular item should be understood to include a plural item, and vice versa, unless expressly stated otherwise or apparent from the context. Grammatical conjunctions are intended to represent any and all disjunctive and conjunctive combinations of coordinated clauses, sentences, words, and the like, unless expressly stated otherwise or apparent from the context. Thus, the term "or" should be generally understood to mean "and / or," and the like.

[0021] References herein to ranges of values ​​are not intended to be limiting, unless otherwise indicated herein, but rather to refer individually to any and all values ​​falling within the range. Each separate value within such range is incorporated into the present specification as if it were individually recited herein. It should also be understood that various numerical ranges and values ​​for material properties are provided and described herein as being suitable for wear-resistant composite materials. These values ​​are derived from a combination of reported material properties, experimental results, and / or estimates based on any of the above and observed wear resistance properties, and are intended to generally describe values ​​or ranges of values ​​within which a composite structure exhibits superior wear resistance compared to its individual components.

[0022] The terms "about," "approximately," or the like, when used in conjunction with numerical values, should be construed to indicate a tolerance as would be recognized by one of ordinary skill in the art to operate satisfactorily for the intended purpose. Value ranges and / or numerical values ​​are provided herein merely as examples and do not constitute limitations on the scope of the described embodiments. Any and all examples provided herein, or the use of exemplary language (such as, for example, or the like), are intended merely to better describe the embodiments and do not impose limitations on the scope of the embodiments or the claims. The absence of language herein should be construed as indicating any non-claimed element as essential to the practice of the embodiment.

[0023] In the following description, terms such as "first," "second," "top," "bottom," "up," "down," etc. are words of convenience and should not be construed as limiting terms, unless specifically stated otherwise.

[0024] The devices, systems, and methods described herein may include or be used with optical sensors, such as any of the retrographic sensors described in U.S. Patent Application No. 14 / 201835, filed March 8, 2014, U.S. Patent No. 9,127,938, granted September 8, 2015, and U.S. Patent No. 8,411,140, ​​granted April 2, 2013, the entire contents of each of which are incorporated herein by reference. In certain embodiments, the devices, systems, and methods described herein may be used in retrographic sensing contact pads for robotic tools, or in retrographic sensors designed for repeated use on wear surfaces. However, the devices, systems, and methods described herein may also or instead be included in or otherwise used with other systems, such as any system that may advantageously incorporate a compliant, wear-resistant contact surface.

[0025] FIG. 1 shows a cross-sectional view of a wear-resistant composite structure. In general, the structure 100 may include a substrate 110 formed of a soft material such as a flexible elastomer, and a membrane 120 formed of a strong, hard material such as a hard elastomeric membrane (film). The membrane 120 may be, for example, a harder elastomer that at least partially covers the substrate 110. For example, the membrane 120 may cover the entire top surface of the substrate 110, thus providing a working surface for using the wear-resistant composite structure 100. The membrane 120 preferably has a relatively low coefficient of friction (COF) to facilitate sliding across the contact surface 130 so as to be wear-resistant. This two-layer composite structure may advantageously form a compliant, wear-resistant contact pad that can conform to a target surface while resisting damage due to contact with wear materials on the target surface. It will also be appreciated that, although elastomers provide a variety of materials with suitable mechanical properties for the substrate 110 and membrane 120, other materials may also be used or may be substituted therefor. For example, the substrate 110 may be formed from a fluid contained within a volume bounded, in whole or in part, by a hard elastomeric membrane 120, or by any other membrane of a suitably strong and resilient material.

[0026] In general, the thin film 120 and the substrate 110 may be supported by a support structure 140 that provides structural and mechanical support to the composite structure 100, for example, so that the composite structure 100 may be positioned or otherwise manipulated for its intended use. For example, the support structure 140 may comprise a rigid, optically transparent plate for use in light detection applications, or a robotic element such as a robot finger or other robotic effector for use in robotic manipulation of a target object using the composite structure 100 as a gripping surface. More specifically, the support structure 140 may comprise any rigid, semi-rigid, or flexible structure, or combination thereof, as appropriate for the intended application. For example, in a retrographic sensor or similar light detection device or system, the support structure 140 may comprise a 10-20 mm thick optically transparent polyethylene terephthalate or polycarbonate that is generally rigid but may also flex somewhat to conform to a target surface, for example.

[0027] FIG. 2 shows the abrasion resistance as a function of film thickness for a composite structure such as that shown in FIG.

[0028] Generally, the x-axis represents the thickness of a rigid thin film disposed on a flexible substrate, such as the thin films described above or any other suitable exterior surface material. This material covers the surface of a flexible underlying substrate, such as a flexible elastomer. The film thickness may be measured using any suitable units for the depth of the rigid thin film on the flexible substrate. For example, the film thickness may be measured in micrometers, centimeters, inches, etc.

[0029] The y-axis indicates abrasion resistance. This can be measured using any suitable metric or figure of merit that increases as resistance to abrasion increases. For example, abrasion resistance can be measured in terms of breakage (tear) or exposure of a flexible elastomer, for example, under standardized continuous abrasion conditions, per unit time. For example, this can be exposing the thin film to an abrasive surface, such as abrasive paper with a given grit moving on a belt abrader at a given speed under a given normal force. In another embodiment, abrasion resistance can be measured as the inverse of the decrease in a measurable property of the thin film, such as the decrease in film thickness, or the decrease in weight or volume of the thin film material, for example, under standardized loading conditions. More specifically, any objective abrasion test method or methods known in the art and suitable for comparing abrasion rates for composites with thin films of various thicknesses can be used to measure abrasion resistance, as contemplated herein.

[0030] As shown by curve 200, the abrasion resistance may vary as a function of the thickness of a hard thin film disposed on a flexible substrate. As will be recognized, the shape of curve 200 is not precise and is not representative of any particular material or combination of materials, and the shape and magnitude of the curve will vary according to the particular material selection and physical configuration. Instead, curve 200 is intended to generally illustrate the unexpected relationship between film thickness and abrasion resistance discovered by the inventors while testing various combinations of materials as described herein. In particular, it is noted that for the relatively thick outer film (far right in FIG. 2), the abrasion resistance of the composite approaches the abrasion resistance characteristics of a thick thin film similar to the bulk material. Conversely, as the depth of the film approaches zero, the abrasion resistance of the composite approaches the abrasion resistance characteristics of the underlying soft elastomer. Between these extremes, there appears to be a range of film thicknesses where the hard elastomeric thin film on the soft elastomeric substrate collectively exhibits a surprising increase in abrasion resistance that exceeds, and in some cases dramatically exceeds, the bulk properties of each material separately. For certain material selections, the improvement in objectively measured wear resistance, such as time to failure or inverse material loss, may exceed 50%, 100%, 200%, or even exceed the wear resistance of the constituent materials. For some combinations of common commercially available elastomers and other materials as described herein, this provides a useful operating range 210 of the composite structure that may be advantageously utilized with good optical performance and improved wear resistance in retrographic detection, tactile detection, robotic manipulation, and the like. The high wear resistance may also be advantageously utilized to fabricate devices for other applications, such as gaskets, fluid seals, and the like. As will be appreciated, the useful operating range may also vary for different intended uses. For example, the second operating range 220 may be suitable for high pressure, high cycle mechanical gaskets.

[0031] Some additional preliminary remarks regarding these composite materials are provided herein, along with detailed experimental data for specific embodiments provided below.

[0032] First, as noted above, the shape of curve 200 is intended to show general relationships, not empirical data, for any particular combination of materials. Thus, for example, while the exemplary curve 200 increases monotonically from both sides to a peak, there may be discontinuities or changes in the polarity of the relationship under certain conditions and / or for certain materials. More specifically, there appears to be a complex interrelationship between the properties of the materials used in the composite, with the effective variables including at least the thickness, strength, elasticity, hardness, and coefficient of friction of the thin film, as well as the hardness of the substrate. While not all combinations of these parameters have been characterized, the general relationships appear to be consistent among the combinations of materials tested. For example, although not shown in FIG. 2, a lower coefficient of friction on the outside of the thin film appears to increase abrasion resistance, and a higher strength and elasticity of the thin film appears to increase friction resistance.

[0033] Second, numerous abrasion resistance tests are known in the art and can be used to compare the abrasion resistance of various materials and composite structures as described herein. For example, the American Society for Testing and Materials (ASTM) abrasion test ASTM D-1044 (also called Taber Abrasion) is a standard test used to determine plastic abrasion resistance. This provides a useful objective benchmark for comparing abrasion rates, but other standardized or custom test protocols can also or instead be utilized if they provide a consistent basis for comparing abrasion rates between different materials and / or composites. However, the quantitative results of the experimental data are expected to vary according to the test technique(s) selected, and the general relationships are expected to remain similar and consistently show composites with significant increases in abrasion resistance across any of the composite's constituent materials individually.

[0034] In general, the membrane may be advantageously formed from a strong, rigid, elastic material. Elasticity (measured, for example, in elastic limit (%), stress at elongation, or the like) characterizes the membrane's ability to bend and stretch to conform to uneven contact surfaces and to reduce or relieve areas of high local stress. Various objective measures of elasticity are provided in Table 2 below. At the same time, when a membrane is particularly desired, for example, so that a composite structure can maintain its structural integrity while deforming, high strength (e.g., tear strength (e.g., kN / m measured per ASTM D624 type C), tensile strength (e.g., MPa measured per ASTM D412), elongation at break (%), or any other objective measure) allows the membrane to undergo these deformations without tearing or otherwise breaking.

[0035] As will be appreciated, some of the material properties described above, such as elongation at break, may be considered measures of strength (e.g., by specifying a breaking point (limit point)) or elasticity (e.g., by specifying a degree of deformability). However, whether a particular metric describes strength or elasticity is generally less important than whether the measured property reliably contributes to the wear resistance of the composite structure (more specifically, by allowing the composite thin film to easily and reliably conform to the contacting surface). Thus, while various measures are categorized herein in measuring strength or elasticity, these should be understood as categories of convenience rather than strict definitional precision. Notwithstanding the above, based on reported data, experimental data, and observations, a useful minimum tear strength for a thin film appears to be about 20 kN / m, or about 20-30 kN / m, where a thin film having a tear strength of 40 kN / m and above provides better wear resistance properties.

[0036] It is also noted that different objective measures of strength and elasticity are generally (although not strictly) correlated with one another such that different objective measures of strength can be used as proxies for identifying high strength materials suitable for wear resistant composites, and different objective measures of elasticity can be used as proxies for identifying high elasticity materials. Furthermore, although the optimal combination of strength, hardness, and elasticity may vary according to other material properties such as the flexibility of the underlying elastomer, roughness characteristics, abrasive contact surface, and other factors, strength and elasticity generally correlate reliably with improved wear resistance performance of different elastomeric thin films having approximately the same hardness.

[0037] These principles may be utilized to particular advantage in certain applications. For example, a retrographic sensor may use a strong thin film disposed on a flexible elastomer. The film is preferably thin enough to allow good conformance to the contact surface of the sensor, having a thickness of 30-80 μm, or more typically about 20-200 μm, or even more typically about 5-500 μm, to provide good physical relief and optical resolution for contact imaging applications. Applicant has realized that this thickness range can also produce the desirable wear resistance qualities described herein. Generally, within these ranges of values, thicker films provide higher wear resistance and lower optical resolution. Thus, in one embodiment, a wear-resistant retrographic sensor is disclosed herein having a thin film layer of 5-500 μm, 20-200 μm, or 30-80 μm, or any other range contained therein, disposed on a flexible elastomer. It is also noted that, as described below, the sensor may also include an optically reflective layer, for example, on the flexible elastomer side of the rigid elastomeric thin film, which may be combined with the rigid thin film to provide a layer (singular) on the flexible elastomer of about 50 to about 100 μm (a thickness within the ranges described above that is useful for high resolution imaging of the contact surface through the rigid thin film). In another aspect, the thin film layer may be formed from an optically reflective layer suitable for retrographic detection, thus eliminating the need for a separate opaque layer disposed thereon. Optical sensors formed from the composite materials described herein may also include adhesives, optical coatings, low friction coatings, rigid substrates, etc., that may be included as additional layers and / or incorporated into the thin film layer (and / or flexible elastomer). Now, one embodiment of a wear-resistant retrographic sensor according to these principles will be described in more detail.

[0038] FIG. 3 shows a cross-sectional view of a system including a wear-resistant composite structure. The structure 300 may be a retrographic sensor having a wear-resistant contact surface and may be integrated into any of the devices and systems described in, for example, U.S. Pat. No. 1,096,5854, which is incorporated herein by reference in its entirety. In this regard, the structure 300 may also include an illumination and imaging system 302 for use in capturing images and performing three-dimensional imaging of a target surface. More specifically, the composite structure(s) described herein may be advantageously utilized in any situation where a deformable wear-resistant contact surface may be useful, such as a gripper, end effector or other mechanical handler that may be used to robotically manipulate items, or the like.

[0039] In the case of a robotic finger with a retrographic sensor, the composite structure may generally include the layers shown in FIG. 3. For example, the structure 300 may include a support 304 formed from an optically transparent rigid material, such as glass or transparent polymethylmethacrylate or polycarbonate. Additionally or alternatively, the support 304 may include a semi-rigid material, a flexible material, or a combination thereof, depending on the intended use of the structure 300. The structure 300 may also include a substrate 306, such as a layer of a flexible, optically transparent elastomer or the like, disposed on the support 304. An adhesive layer 308 may be provided to attach the flexible elastomer of the substrate 306 to one or more additional surface layers. For example, an opaque layer 310, which may include scattering and / or reflective pigments, or may be coated or otherwise treated to provide an opaque surface for imaging, may be bonded to the flexible, transparent, elastomeric substrate 306 by adhesive layer 308 and may form a hard, resilient layer for wear resistance. A friction control layer 312 may be disposed on the opaque layer 310 to further manipulate (manage) the wear resistance properties of the composite material. In another embodiment, the friction control layer 312 may include a hard, resilient, wear resistant layer disposed on the opaque layer 310 that provides the composite material with desired optical and mechanical properties. In one embodiment, the friction control layer 312 may include a low friction layer and a hard, resilient layer that may be formed from a single material, a monolithic material, or multiple layers of materials. In another embodiment, the friction control layer 312 may be formed from a single material or composite material that combines the optical properties of the opaque layer 310, the low friction properties of the friction control layer 312, and the hard, resilient properties of the friction control layer 312, thus providing a single layer of material bonded to or otherwise disposed on the substrate 306.

[0040] As will be appreciated, while Figure 3 illustrates specific layers, structure 300 may more generally include abrasion-resistant soft contact pads formed by covering a soft elastomer (or other material) with a thin film of a harder elastomer (or other material), where the harder elastomer has a relatively low coefficient of friction (COF) (as in structure 100 shown in connection with Figure 1). Such composite materials, when formed from a suitable elastomer, are advantageously more abrasion-resistant than pads composed entirely of either of the constituent elastomeric materials, and may be at least 50% more abrasion-resistant, at least 100% more abrasion-resistant, at least 200% more abrasion-resistant, or more, depending on the material, as objectively measured using any suitable abrasion test or abrasion resistance standard(s). Using various suitable elastomers, such composite materials can be configured for use as, for example, retrographic sensors, having an optically transparent or substantially optically transparent (e.g., within the wavelength range used for imaging) elastomer that is flexible enough to deform against a contacted target surface and a harder, internally disposed opaque layer, and that can be illuminated through the transparent elastomer and imaged to capture data for use in reconstructing a three-dimensional surface.

[0041] The friction control layer 312 may include any suitable low friction layer or composite material directly adjacent to the target surface 314 (e.g., between the target surface and other layers of the structure 300) to enable sliding and to reduce or mitigate points of concentrated contact forces. In one embodiment, a suitable low friction or low static friction surface may be formed on the friction control layer 312 by spray coating. For example, this may include spraying a dilute solution of an (uncured) abrasion resistant coating (e.g., polyurethane with about 10% by weight of acrylate monomers) and about 2% by weight of methylsilsesquioxane microspheres having a diameter of about 10 μm onto the abrasion resistant coating. The spray coating may be applied so that it does not dry flat, leaving an uneven matte surface with contours partially formed by the microspheres to reduce large uniform high friction contact surfaces. The coating may be UV cured to crosslink the binder in the friction control layer 312 to the binder in the opaque layer 310, thus fixing the microspheres on the surface of the composite structure. The underlying opaque layer 310, or another hard, resilient layer between the opaque layer 310 and the friction control layer 312, may also contain microspheres, for example in a similar ratio, to maintain a concentration of friction-reducing microspheres at the interface of the composite structure as the composite structure 300 wears. More generally, a variety of friction and stiction reduction techniques are known in the art and may be adapted to provide low or low stiction interfaces to any of the composite structures described herein.

[0042] In general, the contact pad may be formed from any of the composite structures described herein, which may advantageously exhibit superior abrasion resistance relative to any of the bulk materials forming the composite. For example, the hard thin film may be formed from thermoplastic polyurethane (TPU) having a Shore A hardness of 70, which is relatively hard in this context. If a solid slab of this material is pressed against a belt sander with a 200 grit belt at a given contact force and operated for 60 seconds, a measurable amount of the TPU will be worn away. However, when a 75 μm thick thin film of the same TPU is coated on top of a mass (volume) of soft elastomer, for example having a Shore A hardness of 5 (relatively soft in this context), the composite pad exhibits almost no abrasion under the same contact conditions. More generally, a thin film of TPU, when supported by a soft elastomer, exhibits greater abrasion resistance than a thick slab of the same TPU alone. Figures 4-8 show the working principle of such an abrasion-resistant contact pad.

[0043] Figure 4 shows an uneven (undulating) object RO1 with sharp protrusions at its base. The object is pressed against a hard elastomeric pad HE1 supported on a rigid block RB1. Each protrusion exerts a localized force on the small patch of elastomer it contacts. Because the contact area of ​​each protrusion is small, the localized pressure is high. Now, if the object moves tangentially, large localized stresses will be created at the contact points, which may lead to localized damage as the protrusions rub on the pad.

[0044] FIG. 5 shows an uneven object RO2 being pressed against a soft elastomeric pad SE2 supported by a rigid block RB2. Because the pad is made of a soft material, it easily deforms to conform to the uneven (rough) texture of the object. The contact pressure is distributed over a large surface area rather than concentrated at a few points, thereby reducing the tendency for high local stresses to develop when the object moves tangentially. However, soft elastomers generally have a high COF that increases the tangential force during tangential movement. Furthermore, soft elastomers are generally mechanically weak and thus easily damaged, resulting in significant wear or damage when sliding under these conditions.

[0045] Thus, pads made from either hard or soft elastomers are both susceptible to damage from uneven objects rubbing across their surfaces, but for different reasons. Hard elastomers have the advantage of being strong and having a low COF, but the disadvantage of high local stress at few contact points. Soft elastomers have the advantage of distributing the force over a large area, thereby preventing high local stress points, but the disadvantage of being weak and having high friction.

[0046] FIG. 6 shows a wear-resistant contact pad in contact with a rough surface. Typically, a thin film of hard elastomer may cover a soft elastomer. A rough object RO3 is pressed against the composite pad, which is made of a hard elastomer thin film HEF3 coated on a soft elastomer base SE3 supported by a rigid block RB3. If the thin film is thin and elastic, it will easily flex and stretch to follow the contours of the rough object, thereby allowing the force to be distributed over a large area. At the same time, the thin film has the strength and low COF associated with hard elastomers, thus resisting wear.

[0047] FIG. 7 shows a contact pad with a thicker thin film of hard elastomer. In general, an uneven object RO4 may come into contact with a hard elastomer thin film HEF4 coated on a soft elastomer base SE4 supported on a rigid block RB4. This thin film HEF4 is much thicker than the corresponding thin film HEF3 of the previous example. As a result of the excessive thickness, the thin film is not flexible and stretchable enough to follow the contours of the uneven (rough) surface of the object. This leads to a sparse set of contact points with high local stresses. Thus, an excessively thick hard elastomer thin film increases the tendency to forcefully engage sharp or uneven contact features and damage the contact pad. This also corresponds to the right tail of the wear resistance curve shown in FIG. 2, where the wear resistance of the composite structure approaches that of the thin film as the film thickness increases.

[0048] In another embodiment, membranes using very hard elastomers do not provide the best performance. Figure 8 shows an uneven object RO5 in contact with a very hard elastomer membrane VHEF5 coated on a soft elastomer SE5 mounted on a rigid block RB5. Even if this membrane VHEF5 were just as thin as the membrane HFE3 of Figure 6, it would be too stiff to follow the contours of the uneven object, resulting in a sparse collection of contact points with high local stresses that could damage the contact pads. Thus, if a very high hardness implies low elasticity, or more generally, an inability to conform to the target surface, this may compromise the wear resistance of the composite structure.

[0049] In the above, terms such as "strength" or "high strength" are used to describe various elastomers. As will be appreciated, there are multiple ways to specify the strength of a material, including tensile strength and tear strength. When a rough object moves across an elastomeric pad, multiple aspects of mechanical strength may be important. While these various strength measurements generally correlate, they are not universally so, and it may be important in some cases to ensure that several different strength metrics are sufficient collectively for good abrasion resistance. Thus, when terms such as high strength, stronger, etc. are used herein, they should be understood to also mean specific objective strength metrics, such as any of those described herein, where the material properties are sufficient to ensure good abrasion resistance, as well as any combination of strength metrics that enable the composite structure to function as a wear-resistant contact pad.

[0050] Additionally, although the general term "friction" is used, it is understood that friction can be static or dynamic, and that frictional interactions are nonlinear in ways not captured by the coefficient of friction (COF). Additionally, friction is a property of two particular materials contacting each other, and the frictional force against one material, such as glass, may be different than the frictional force against another material, such as steel. At the same time, the coefficient of friction is useful for correlation, such that it makes sense to talk about different elastomers having, for example, a higher or lower COF for the particular type of target surface for which the composite structure is intended.

[0051] The parameters shown to affect the wear resistance of composite structures are now considered.

[0052] Since the flexible substrate supporting the rigid thin film does not itself come into direct contact with the object, the COF of the flexible substrate is not at all critical to the composite structure remaining intact. However, hardness, measured, for example, on the appropriate Shore hardness scale, is a relevant metric for good abrasion resistance. For substrates, a variety of flexible elastomer families have been tested, including thermoplastic elastomers such as silicone rubber (PDMS), polyurethane, and styrene block copolymers. Any of these would function adequately as substrates for contact pads, provided they are adequately flexible. For example, useful abrasion-resistant composite contact pads have been fabricated and tested using flexible elastomers with Shore A hardnesses of less than 10, although harder elastomers may be used in various situations (e.g., when a modest reduction in abrasion resistance is acceptable or when a harder and / or lower friction thin film is utilized). On the Shore 00 scale, useful flexible elastomers for abrasion-resistant contact pads appear to range from 25 to 65. Experimental data does not suggest any lower limit of this hardness, so other additional soft gels, fluids such as non-viscous fluids, gases, or the like may also or instead be used as the base material for the wear-resistant composite.

[0053] For coating films, relevant parameters may include thickness, hardness (e.g., measured on the Shore hardness scale), strength (e.g., measured on tear strength, tensile strength, or similar objective measure(s)), elasticity (e.g., measured on yield elongation, elastic limit, stress at extension, etc.), and coefficient of friction (e.g., kinetic or static coefficient of friction). With respect to hardness, composite contact pads using elastomers with hardnesses of about Shore A50 to Shore A90 have shown improved wear resistance (relative to the constituent materials). For a given hardness, various elastomers have different combinations of strength, COF, and elasticity, resulting in different friction resistance properties. For high friction resistance, a hard elastomer is generally considered useful because it is strong and because it has a low COF.

[0054] The coefficient of friction of the outer hard film can greatly affect the wear resistance. For many materials, the kinetic coefficient of friction was measured against brushed stainless steel, more specifically, a 4.5 inch (11.43 cm) stainless steel drum with a fine sand surface rotating at 60 RPM. A 48 inch (121.92 cm) long hollow acrylic rod with a square cross section held the test samples. Each sample was attached to the center point of the rod with polyurethane grip tape. The mounted sample was brought into contact with the rotating drum. The gravitational force from the rod was defined as the normal force F1, which was measured to be 2.1 Newtons. A spring dynamometer was used to measure the resulting friction force F2. The kinetic coefficient of friction was calculated as F2 / F1. Notably, both the Elastollan® TPU film and the Elkem PDMS film have the same hardness (Shore A70), but the friction coefficient of the PDMS is over 300% higher than that of the TPU. All other things being equal, this suggests that TPU will result in composite structures with superior abrasion resistance, a result that was confirmed experimentally. [Table 1]

[0055] In summary, the choice of elastomer for the flexible substrate does not seem to be important as long as it is sufficiently flexible. The choice of elastomer for the hard film seems to be important where the abrasion resistance of the resulting composite depends on a combination of hardness, strength, elasticity and coefficient of friction. At least two elastomers with favorable properties have been experimentally shown to provide good abrasion resistance in composite pads, namely polyurethane and nitrile rubber. As will be generally understood, the terms "soft" and "softer", as well as the complementary terms "hard" and "harder", are used to describe the relative hardness (or flexibility) of the base elastomer in the substrate and the coating film, and more specifically to suggest that the base elastomer is relatively softer and more pliable than the coating film. Some general ranges of flexibility and hardness are provided herein by objective measurement using the Shore scale, however, other flexibility and hardness of materials may be used, provided that the composite structure has a substrate that is flexible enough to create and reduce loose contact points with generally uneven surfaces, and has a thin, low friction, resilient surface that is hard enough to conform to the contacting surface to distribute the surface contact and resulting contact forces. Thus, although specific numerical ranges are provided, other ranges and / or other elastomers or the like may also be used in combination to provide a wear resistant composite structure, and are intended to be within the scope of this disclosure, unless expressly noted to the contrary.

[0056] Given these general constraints, polyurethanes and nitriles, among others, are believed to offer suitable properties for wear-resistant composites. Polyurethanes generally have high strength, low coefficients of friction, and high elasticity and are believed to function well as coating films. For example, polyurethane elastomers with a Shore A hardness of 40-90 typically have elongations at break of over 400%.

[0057] Nitrile rubber is also quite worthy in these dimensions. Most of the other elastomer families are considered to be unable to reach these objective metrics and provided less than satisfactory abrasion resistance under the test conditions when tested in composite structures. For example, PDMS is generally weaker than polyurethane and nitrile and has a higher COF than polyurethane or nitrile. Thus, PDMS performs worse than these two preferred materials in at least two dimensions and performs worse as an abrasion-resistant coating for flexible elastomers. Latex membranes, such as those used in disposable rubber gloves, have high strength and high elasticity, but also a high COF. Flexible PVC membranes, such as those used in disposable vinyl gloves, have a low COF but low strength and low elasticity. Thermoplastic elastomers, such as SEBS or SEEPS styrene block copolymers, have high strength and high elasticity, but a high COF.

[0058] A number of examples are now provided. A number of substrates were constructed from a flexible PDMS elastomer (Ecoflex® Gel from Smooth-on) covered with various hard elastomer films. Eco-flex Gel is extremely tacky, so the films can be directly attached to the substrate without the need for any additional binder. Films with various properties were obtained from commercial sources, as identified below. PDMS films were formed as coatings on glass plates using LSR Silbione® 4370, 1 part A, 1 part B, and 4 parts hexamethyldisiloxane from Elkem. After drying and curing, the films were approximately 75 μm thick. To create the TPE films, SEEPS block copolymer (Septon® 4099 from Kuraray) was mixed with mineral oil in a ratio of approximately 1:1 and diluted with toluene in a ratio of approximately 1:4. This was poured onto a glass plate to form a thin film of Shore A70 that was approximately 75 μm thick after drying. To make the Elastoran® TPU thin film, Elastoran® 1170A10 (from BASF) was dissolved in tetrahydrofuran and poured onto a glass plate to form a thin film of approximately 80 μm thick after drying. The abrasion resistance of these substrate-thin film composite pads was tested by pressing them with a 200 grit abrasive belt against a belt sander operating at 1900 feet (579.12 m) per minute (fpm) with a 20 gram weight. If the thin film wears under these conditions, it will eventually reach a point of catastrophic failure and tear as the abrasive paper breaks through to the underlying soft elastomer. The time to failure is as follows: [Table 2]

[0059] Based on the above measurements and the reported properties of various corresponding materials, the thin films performed better, where they had high strength, high elasticity, and low friction. In one aspect, polyurethanes, and more specifically, thermoplastic polyurethanes, which have high hardness, high elongation at break, and high tensile strength, provide suitable materials for wear-resistant composites, as described herein.

[0060] A second set of experiments was performed utilizing a composite structure as shown in Figure 3. Polyurethane, polyurethane and acrylate blends, and nitrile rubber were tested as abrasion-resistant films. For this test, the soft elastomer included SEPTON® 4033, a thermoplastic elastomer manufactured by Kuraray, a SEEPS polystyrene block copolymer, plasticized with additives such as mineral oil and Regalrez® 1094, a tackifier manufactured by Eastman Chemical Co. The plasticizer level was 80% by weight of the soft gel with 40% from mineral oil and 40% from tackifier. The hardness of the soft gel was measured as Shore 00 = 33. The thickness was 3 mm. Both the adhesive layer and the reflective layer were prepared with BASF Elastollan® polyurethane 1170A10 for a combined thickness of 15 μm. The reflective pigment was Sparkle Silver Ultra® 7908 manufactured by Silberline.

[0061] The properties of the polyurethanes tested are summarized below in Tables 1 and 2. Generally, the American Society for Testing and Materials (ASTM) abrasion test ASTM D-1044 (also known as Taber Abrasion) is a standard test used to determine the abrasion resistance of plastics. Although various standardized abrasion tests are known in the art, this provides a useful benchmark for the properties of the various elastomeric materials described herein. [Table 3] [Table 4]

[0062] Acrylates can be used to modify the hardness and elasticity of polyurethanes. Acrylates can be particularly useful because they have been shown to be molecularly compatible with polyurethanes and capable of forming interpenetrating 3D networks upon polymerization. Such 3D networks can add strength and stiffness to the material and facilitate bonding of such layers by chemically crosslinking the material across adjacent layers. The 3D crosslinked network results from polymerization of the acrylate groups, which can be easily achieved by incorporation of a UV initiator into the composition and UV irradiation after coating or casting. Acrylates are available in a wide range of chemical compositions, including chemical structures, molecular weights, and numbers of acrylate functional groups per molecule. The strength of the interpenetrating 3D network depends on the crosslink density of the network, which can be controlled by the functionality or number of acrylate groups per molecule, the molecular weight between the acrylate groups, and the mass concentration of the acrylate used to form it. Difunctional polyurethane acrylates, which are linear polyurethane oligomers with an acrylate group at the end of each molecule, can be particularly effective. These materials form homogeneous networks with polyurethanes. Thus, in one embodiment, polyurethanes can be modified with the addition of one or more acrylates to improve hardness and elasticity, and to improve the resulting wear resistance properties of composite structures using polyurethane / acrylate blends.

[0063] Table 3 below summarizes the properties of Sartomer's acrylate urethane oligomer that have been found to be favorable upon testing. Note that as a polymerized homogeneous material, it has an elongation of 140%, significantly less than the 600% to 800% elongation of the polyurethanes with which it is mixed. Also, the tensile strength is similar to polyurethanes. Thus, mixing acrylates with polyurethanes can be used to add stiffness, and its polymerization can be used to bond adjacent layers containing acrylates. [Table 5]

[0064] Samples of polyurethane and polyurethane acrylate mixtures to be tested were coated onto glass plates from the solvent THF (tetrahydrofuran). The coatings were peeled from the glass, cut to shape, and placed on top of the reflective layer of the composite structure to be tested. The coatings were held in place by simple sticking or the tendency of two smooth surfaced samples to adhere upon contact. Nitrile rubber samples were manually held in place for testing.

[0065] The abrasion resistance of contact pads formed using materials described herein was evaluated in a manual test by abrading the surface of the composite pad with a belt sander at a speed of 40 inches (101.6 cm) / second and 120 grit abrasive paper. The surface of each sensor was dome-shaped with a radius of curvature of approximately 3 inches (7.62 cm). The dome-shaped sensor surface was held by hand against the moving abrasive paper belt using a light to apply sufficient pressure so that the circular portion, approximately 3 / 8 inch (9.525 mm) in diameter, contacted the moving abrasive paper belt.

[0066] The elasticity of each sample was also evaluated by a simple test referred to herein as the experimental elastic limit. For this test, strips of thin film were cut to 1 cm width and stretched parallel to a tape measure to record the length at which the strip exhibited significant resistance to further stretching. This stretch is considered to be approximately the point at which the polymer chains stretch or unwind to their limits such that further stretching would cause the molecular bonds to pull or break. It should be noted that the experimental elastic limit as measured here is not the same measurement as the elasticity at break, which is the percentage of stretch at which the material yields, or the traditional elastic limit, which is the point at which a material plastically or permanently deforms and loses its ability to elastically return to its original state. Although all of these measurements are generally correlated, the elasticity at break is significantly greater than the experimental elastic limit. [Table 6]

[0067] Note, as shown in Table 4, that the acrylate concentration associated with the best performance is currently determined to be 0% acrylate, and the rate of film loss from polishing at this level is significantly lower (approximately 0-0.25 μm per minute for polishing with 120 grit paper moving at 40 in / sec). A 100 μm thick film, which is reasonable for a robotic finger, would survive several hours of exposure to this type of polishing.

[0068] Also, note from Table 4 that abrasion resistance decreases in progressing through the material series as the polyurethane hardness increases, which is counter to common sense. Note from Table 1 above that the abrasion resistance of solid polyurethanes increases in progressing through the softer to harder Elastollan® grades. This improved abrasion resistance with increasing hardness is common for solid elastomers.

[0069] It should also be noted that the addition of urethane acrylates reduces the abrasion resistance. The acrylates are difunctional, i.e., they have two acrylate groups per molecule, and when exposed to UV radiation in the presence of a UV initiator, they crosslink themselves forming three-dimensional structures that result in increased hardness and decreased elasticity of the polymerized or UV-cured mixture. In the case of solid samples, one would expect the presence of acrylate 3D structures to improve abrasion resistance, since they increase strength just as elastolane with higher hardness has higher strength, but exactly the opposite has been observed (reduced abrasion resistance).

[0070] Two samples of nitrile rubber were tested and the data is summarized in Table 5 below. [Table 7]

[0071] For this test, the nitrile rubber samples were obtained from samples cut from laboratory gloves. A section taken from the thumb of the glove was stretched over a dome-shaped robotic finger sensor, which allowed the sample to be held in place while the surface thus formed was subjected to an abrasion test. The results show abrasion resistance that is remarkably good and similar to that found for many samples of combined polyurethane / acrylate, even if not as good as the pure polyurethane samples. It should also be noted that the two samples tested are quite different in thickness, but the abrasion resistance is comparable between the two samples. If these same samples were stretched over a dome-shaped hard acrylate shape like a convex lens and held against an abrasive belt, they would be useless within seconds due to tearing.

[0072] Figure 9 shows the wear rate versus elasticity for various composite materials. More specifically, Figure 9 shows the wear rate (μm / min) as a function of experimental elastic limit measured for various materials used as coating thin films. It should be noted that wear performance (e.g., reduction in wear rate) generally correlates to experimental elastic limit, where the best wear resistance is provided by the thin film with the highest experimental elastic limit (e.g., most elastic).

[0073] Contact pads made with composite structures as described herein may be used in a variety of applications. For example, they may be used in robotic fingers or other hand tools. However, non-rigid wear-resistant contact pads may be usefully deployed in many other situations. For example, such pads may be used in any situation where a soft or flexible object is in frictional contact with a second object, especially in the absence of a liquid lubricant. For example, the composite structure may be used as a seal for a moving cylindrical shaft. In such an embodiment, the chamber may be sealed to prevent gas from inside the chamber from mixing with gas from outside the chamber. The shaft may penetrate the wall of the chamber via an elastomeric annular seal, which, if made with a composite structure as described herein, may allow the shaft to rotate about or translate along its axis while minimizing wear. More generally, wear-resistant composites may be formed into gaskets or other fluid seals for moving parts, or any other gaskets, seals, wipers, or other components where wear resistance is desired for mechanically loaded interfaces.

[0074] In accordance with the above, a wear-resistant composite structure is described herein.As a more specific example, in one embodiment, a device for wear-resistant contact with a target surface, having substantially improved wear-resistant properties as described herein, includes a support structure; a substrate disposed on the support structure, having a first Shore A hardness of 10 or less and a first thickness of at least 1 mm; and a thin film disposed on the substrate for contacting the target surface, the thin film having a second Shore A hardness of at least 70, a second thickness not exceeding 200 μm, a tensile strength of at least 30 MPa, an elongation at break of at least 650%, and a dynamic friction coefficient against matte steel not exceeding 1.5.

[0075] Additionally or alternatively, usefully improved wear resistance performance may be obtained by a composite device including a support structure; a substrate disposed on the support structure and having a first Shore A hardness of 10 or less and a first thickness of at least 1 mm; and a thin film disposed on the substrate for contacting a target surface, the thin film having a second Shore A hardness of at least 50, a second thickness not exceeding 500 μm, a tensile strength of at least 10 MPa, an elongation at break of at least 300%, and a dynamic coefficient of friction against matte steel not exceeding 1.5.

[0076] In these and other embodiments, the thin film may include, for example, a thermoplastic polyurethane, a thermosetting polyurethane, or a nitrile rubber. The substrate may include, for example, at least one of polydimethylsiloxane (PDMS), polyurethane, and a thermoplastic elastomer. It is also recognized that the phrase "disposed on" as used in the preceding description does not require direct contact between the two recited layers. That is, although the thin film is described as being disposed on the substrate, this does not require direct contact between the two layers or exclude an intervening functional layer or the like. Instead, when one layer or structure is described as being disposed on another, this allows for and optionally includes one or more intervening layers, including functional layers, such as optical films, adhesive layers, patterned or textured surfaces, and the like.

[0077] Also disclosed herein is a method for fabricating a wear-resistant composite material. This generally includes providing a support structure, such as any rigid or flexible support structure appropriate for the intended application. This may include, for example, a robotic finger, a lens or other optical element, a substrate for a retrographic sensor, a gasket, a contact pad, a wiper, and the like. The method may include disposing a substrate on the support structure, the substrate including a first elastomer having a first hardness. The method may also include disposing a thin film of a second elastomer on a first surface of the first elastomeric substrate, the second elastomer having a second hardness greater than the first hardness of the first elastomer, the second elastomer having a low coefficient of friction on a second surface facing away from the first surface of the first elastomeric substrate, and the second elastomer having a high strength and high elasticity. In general, the support structure, elastomer, substrate, and thin film may be any as described herein. It will also be appreciated that the methods may include any suitable manufacturing technique, such as casting, spin-coating, mixing, curing, bonding, etc., each consistent with the desired resulting composite material. All such techniques suitable for producing composite wear-resistant structures as described herein are intended to fall within the scope of the present manufacturing methods.

[0078] The steps of the methods of the embodiments described herein are intended to include any suitable manner in which such steps are performed, unless a different meaning is clearly provided or otherwise apparent from the context, and are consistent with the patentability of the claims that follow. Thus, for example, performing step X includes any suitable manner in which another party, such as a remote user, a remote processing source (e.g., a server or cloud computer), or a machine, performs step X. Similarly, performing steps X, Y, and Z may include any manner of directing or controlling any combination of other entities or resources involved in performing steps X, Y, and Z to obtain the benefit of such steps. Thus, the steps of the methods of the embodiments described herein are intended to include any suitable manner in which one or more other parties or entities perform such steps, unless a different meaning is clearly provided or otherwise apparent from the context, and are consistent with the patentability of the claims that follow. Such parties or entities need not be under the direction or control of any other party or entity, and need not be located within any particular jurisdiction.

[0079] It is recognized that the above-described devices, systems, and methods are described by way of example, and not by way of limitation. Unless expressly indicated to the contrary, the disclosed steps may be modified, added, deleted, and / or rearranged without departing from the scope of the present disclosure. Numerous variations, additions, deletions, and other modifications will be apparent to those skilled in the art. Moreover, the order or presentation of the method steps in the above description and drawings is not intended to require this order of performing the recited steps, unless a particular order is expressly required or otherwise apparent from the context. Thus, while specific embodiments have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the present disclosure, which are intended to form part of the present invention as defined by the following claims. The following claims are to be interpreted in the broadest sense permitted by law.

Claims

1. 1. A device for abrasion-resistant contact with a target surface, comprising: a support structure; a substrate disposed on the support structure, the substrate comprising: a first Shore A hardness of 10 or less; and a substrate having a first thickness of at least 1 mm; a thin film disposed on the substrate for contacting the target surface, the thin film comprising: a second Shore A hardness of at least 50; a second thickness not exceeding 500 μm; a tensile strength of at least 10 MPa; an elongation at break of at least 300%, and A device having a dynamic coefficient of friction against matte steel not exceeding 1.

5.

2. The device of claim 1 , wherein the thin film comprises a thermoplastic polyurethane, a thermoset polyurethane, or a nitrile rubber.

3. a substrate comprising a first elastomer having a first hardness; a thin film comprising a second elastomer covering the first surface of the substrate of the first elastomer, the second elastomer comprising: (a) a second hardness of the first elastomer that is greater than the first hardness; (b) high strength, and (c) a low coefficient of friction on a second surface of the first elastomer facing away from the first surface of the substrate.

4. The device of claim 3 , wherein the increased strength of the second elastomer comprises a greater tensile strength than the first elastomer.

5. The device of claim 3 , wherein the increased strength of the second elastomer comprises a greater tear strength than the first elastomer.

6. The device of claim 3 , wherein the first elastomer and the second elastomer are configured to provide a wear-resistant elastomeric pad.

7. The device of claim 3 , wherein the first elastomer has a Shore A hardness not exceeding 20.

8. The device of claim 3 , wherein the first elastomer has a Shore A hardness not exceeding 5.

9. The device of claim 3 , wherein the second elastomer has a Shore A hardness of at least 30.

10. The device of claim 3 , wherein the second elastomer has a Shore A hardness of at least 50.

11. The device of claim 3, wherein the thin film has a thickness of 5 μm to 1000 μm.

12. The device of claim 3, wherein the thin film has a thickness of 20 μm to 400 μm.

13. The device of claim 3 , wherein the thin film has a thickness not exceeding 500 μm.

14. The device of claim 3 , wherein the thin film has a thickness not exceeding 200 μm.

15. The device of claim 3 , wherein the substrate of the first elastomer has a thickness greater than 500 μm.

16. The device of claim 3 , wherein the first elastomer is optically transparent, and the device further comprises a rigid, optically transparent support structure for the first elastomer.

17. The device of claim 3 , wherein the thin film comprises a low-friction coating.

18. The device of claim 3 , wherein the second surface of the thin film provides a contact area having a combined wear resistance greater than the wear resistance of the first elastomer alone or the second elastomer alone.

19. 20. The device of claim 18, wherein the composite abrasion resistance is at least 50% greater than the first elastomer alone or the second elastomer alone.

20. 20. The device of claim 18, wherein the composite abrasion resistance is at least 100% greater than the first elastomer alone or the second elastomer alone.

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