Patent Application
20140209229
The present invention relates to a cushioning device including a layer of styrenic based gel material having top and bottom surfaces, a first layer including: i. layer of maleic anhydride (MAH), and ii. layer of thermoplastic polyurethane (TPU), wherein the first layer has a surface bonded to the top surface of the layer of styrenic based gel material, and the second layer has a surface bonded to the bottom surface of the layer of styrenic based gel material and a pressure sensitive adhesive coating is disposed on at least one of the first and second layers opposite to the layer of styrenic based gel material.
Cushioning devices made of soft gels are desirable for their comfort, flexibility, durability and look. Generally, such cushioning devices include a gel material having at least one layer of polyurethane film thereon that contacts the foot, sock or hosiery of the user and a pressure sensitive adhesive on the opposing side of the cushioning device that is in contact with the footwear of the user.
To effectively improve the comfort of users, soft gel cushioning devices require a certain level of tack to stay in place. For example, to prevent footwear from rubbing sensitive areas of skin (e.g., the heel area) soft gel cushioning devices must stay in place firmly during movement associated with normal use of footwear. However, tack of cushioning devices is reduced over time thereby rendering the cushioning device less effective.
Thus, there is a need for improved cushioning devices having a desirable level of tack that is retained for a greater period of time.
The present invention provides cushioning devices including a layer of styrenic based gel material having top and bottom surfaces, a first layer including: i. layer of MAH, and ii. layer of TPU, and a second layer including: i. layer of MAH, and ii. layer of TPU, wherein the first layer has a surface bonded to the top surface of the layer of styrenic based gel material and wherein a pressure sensitive adhesive coating is disposed on at least one of the first and second layers opposite to the layer of styrenic based gel material
Advantageously, such cushioning devices provide a desirable level of tack which is retained for an extended period of time (e.g., following at least 3-months accelerated aging at 50° C.).
Additionally, desirable film surface friction is provided by cushioning devices wherein at least one of the first and second layers includes: iii. layer of MAH. Notably, the friction coefficient of the iii. layer of MAH in such cushioning devices is less than that of ii. layer of TPU in a film material.
Further, enhanced bonding strength is exhibited by a layer of a terpolymer having ethylene, butyl acrylate and MAH bonded to a layer of TPU as compared to a layer of MAH grafted linear low density polyethylene (MAH-LLDPE) bonded to a layer of TPU.
The present invention also provides methods for providing enhanced adhesion performance of a cushioning device in a shoe including providing the aforementioned cushioning devices wherein the pressure sensitive adhesive is positioned so as to attach the cushioning device inside of the shoe.
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Styrenic based gel materials suitable for use in the present invention include, but are not limited to, the Kraton family of styrene-olefin-rubber block copolymers. In certain embodiments, elastomers are a Kraton block copolymer of styrene-isoprene-styrene (SIS), styrene-isobutylene-styrene (SIBS), styrene/ethylene-co-butylene/styrene (SEBS) or styrene/butadiene/styrene (SBS), and combinations of two or more thereof. In one embodiment, the gel material is a Kraton block copolymer of styrene/ethylene-co-butylene/styrene (SEBS). In certain embodiments, the styrenic based gel material includes mineral oil incorporated into the matrix as a plasticizer.
In one preferred embodiment, the gel material is a Kraton block copolymer of styrene/ethylene-co-butylene/styrene (SEBS) with mineral oil incorporated into the matrix as a plasticizer.
As used herein, TPU will be understood to encompass polymers that contain a plurality of urethane linkages and comprise either aliphatic or aromatic isocyanate prepolymers, and combinations thereof, both with either di- or tri-functional polyol polymers or prepolymers. The TPU may optionally also contain other kinds of chemical linkages formed from the reactions of polyisocyanates, including but not limited to urea linkages, isocyanurate linkages, oxazolidone linkages, biuret linkages, allophanate linkages, combinations of these, and the like.
The gel materials useful in the invention may typically have a Shore 00 hardness of between about 10 and about 80. In certain embodiments, the gel materials used may have a Shore 00 hardness of between about 30 and about 60. In certain embodiments, the gel materials used may have a Shore 00 hardness of about 50. The gel materials may typically have a thickness of between about 1 and about 7 mm. In certain embodiments, the gel materials used may typically have a thickness of 2.5 mm.
The film material includes i. layer of MAH and ii. layer of TPU. In certain embodiments, each i. layer of MAH independently includes (i) MAH-LLDPE, (ii) a terpolymer having ethylene, butyl acrylate, butyl acetate or ethyl acetate, and maleic anhydride, or (iii) a combination of (i) and (ii). In one embodiment, the i. layer includes MAH-LLDPE.
In certain embodiments, the film material has a thickness ratio of the i. layer to the ii. layer of between 1:3 and 3:1. In certain embodiments, the i. and ii. layers of the film material have a thickness ratio of i. layer to ii. layer of between 1:1 and 1:2. For example, one or both of the first and second layers of the film material may have a thickness of i. layer of MAH that is about 0.04 mm and a thickness of ii. layer of TPU that is about 0.08 mm. Alternatively, one or both layers of the first and second layers of the film material may have a thickness of i. layer of MAH that is about 0.02 mm and a thickness of ii. layer of TPU that is about 0.04 mm.
In certain embodiments, the i. and ii. layers of the film material in the cushioning device will have a thickness of about 0.5 mm. In certain embodiment, the i. and ii. layers of the film material in the cushioning device may have a total thickness of about 0.4 mm. In certain embodiments, the i. and ii. layers of the film material in the cushioning device will have a thickness of 0.2 mm.
In certain embodiments, at least one of the first and second layers of the film material further includes iii. layer of MAH. For example, the iii. layer of MAH includes (i) maleic anhydride grafted linear low density polyethylene, (ii) a terpolymer having ethylene, butyl acrylate, butyl acetate or ethyl acetate, and maleic anhydride, or (iii) a combination of (i) and (ii).
In certain embodiments, the film material has a thickness ratio of the i. layer to the ii. layer of between 1:3 and 3:1 and a thickness ratio of the ii. layer to the iii. layer of between 3:1 and 1:3. In one embodiment, the i. layer, ii. layer and iii. layer of the film material in the cushioning device has a thickness ratio of 1:1:1.
In one embodiment, the film material has i. layer of MAH-LLDPE, ii. layer of TPU and iii. layer of MAH-LLDPE. In another embodiment, the film material has i. layer of MAH-LLDPE, ii. layer of TPU and iii. layer of a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH. In yet another embodiment, the film material has i. layer of a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH, ii. layer of TPU and iii. layer of MAH-LLDPE. In still yet another embodiment, the film material has i. layer of a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH, ii. layer of TPU and iii. layer of a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH. In yet still another embodiment, the film material has i. layer of MAH-LLDPE and/or a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH, ii. layer of TPU and iii. layer of MAH-LLDPE and/or a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH.
In one embodiment, the i. layer, ii. layer and iii. layer of the film material in the cushioning device each have a thickness of about 0.08 mm. For example, in one embodiment, the film material has i. layer of MAH-LLDPE with a thickness of 0.08 mm, ii. layer of TPU with a thickness of 0.08 TPU and iii. layer of MAH-LLDPE with a thickness of 0.08 mm.
Suitable materials for use in the present invention in each layer of MAH independently include (i) MAH-LLDPE; (ii) a terpolymer having ethylene, butyl acrylate, butyl acetate or ethyl acetate, and maleic anhydride, or (iii) a combination of (i) and (ii). In certain embodiments, the i. layer of MAH includes MAH-LLDPE. In certain embodiments, the iii. layer of MAH includes a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH. In certain embodiments, either or both the i. layer of MAH and iii. layer of MAH includes a combination of MAH-LLDPE and a terpolymer of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH. Such combinations can readily be achieved by blending components as is well known to a skilled artisan.
The MAH content of MAH-LLDPE is about 1% or less. The MAH content of suitable terpolymers of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH is 1 to 4% (e.g., greater than 1 wt % to 4 wt %).
Exemplary suitable terpolymers of ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH include, but are not limited to, Lotader® 3210 resin (a random terpolymer of ethylene, butyl acrylate and MAH having a 3% MAH content), Lotader® 3410 resin (a random terpolymer of ethylene, butyl acrylate and MAH having a 3% MAH content), Lotader® 4210 resin (a random terpolymer of ethylene, butyl acrylate and MAH having a 3.8% MAH content, Lotader® 2210 (a random terpolymer of ethylene, acrylic ester and MAH having a 2.8% MAH content), and Lotader® 2308 (a random terpolymer of ethylene, acrylic ester and MAH having a 1.5% MAH content), all of which are available from Arkema, Colombes, France.
In one embodiment, when an SEBS gel material is used in the cushioning device, the ii. layer of TPU includes SEBS. The ii. layer of TPU may typically have a Shore A hardness of between about 40 to about 95. The ii. layer of TPU may typically have a thickness of between 0.025 mm and 0.25 mm.
In certain other embodiments, individual layers of the film material in the cushioning device will have different thicknesses. In practice, varying the thickness of the film material will affect the softness and flexibility of the film material and will likewise affect the softness and flexibility of the final cushioning product.
As used herein, pressure sensitive adhesives (also known as contact adhesives) are those that form viscoelastic bonds that are aggressively and permanently tacky, adhere without the need of more than slight pressure, and require no activation by water, solvent or heat. Pressure sensitive adhesives are typically available in solvent and latex or water based forms and are often based on non-crosslinked rubber adhesives, acrylics or polyurethanes.
In certain embodiments of the invention, the pressure sensitive adhesives may comprise acrylic and methacrylate adhesives, rubber-based pressure sensitive adhesives, styrene copolymers such as styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) copolymers with at least one tackifier, and silicones. Acrylic adhesives often use an acrylate system such as ethylene ethyl acrylate (EEA) or ethylene methyl acrylate (EMA) copolymers, which are used to form hot melt PSA adhesives. Natural rubber, synthetic rubber or elastomer adhesives may typically comprise a variety of materials such as silicone, polyurethane, chloroprene, butyl, polybutadiene, isoprene or neoprene. Rubber and elastomers are characterized by their high degree of flexibility and elasticity.
In certain embodiments, the pressure sensitive adhesive material may include acrylate-based adhesive materials. The thickness of the layer of the pressure sensitive adhesive material may be varied by those of ordinary skill in the art according to the adhesive material used and the desired tack. In certain embodiments, the pressure sensitive adhesive may have a thickness of between about 0.012 mm and about 0.075 mm. In certain embodiments, the pressure sensitive adhesive will have a thickness of 0.012 mm.
In one embodiment, probe tack is at least about 300 g. In certain embodiments, probe tack is at least about 300 g following incubation at 50° C. for at least 3 months.
Although desirable for use in cushioning devices, it is known that gel materials such as SEBS do not readily bond to a TPU film. To overcome this limitation, a film material, including a layer of TPU and layer of MAH, was utilized. The film material was manufactured by a co-extrusion process. The layer of MAH serves as an anchoring layer for the SEBS gel so that the SEBS gel can be bonded to the film material having a TPU layer on the opposing surface to that bound to the SEBS gel. The film material is used as a covering for the SEBS gel. Desirably, the delamination strength between a gel material comprising SEBS and a film material including a layer of MAH and a layer of TPU was found to be about 1.5 lb/in which is sufficient for applications associated therewith.
An injection molding process may be used in a manner well known in the art to bond the layer of MAH of the film material to the SEBS gel. Specifically, in preparation for injection molding, a film material is placed next to the SEBS gel with the layer of MAH of the film material facing the SEBS gel. Additionally, prior to injection molding, a pressure sensitive adhesive is applied to one TPU layer side of the film material. The mold can be treated to resist bonding of the pressure sensitive adhesive or a release liner material can be applied in the mold before application of the pressure sensitive adhesive. Typically, the mold temperature is between 160° C. and 210° C. and the cycle time is approximately 1 min.
The products of the invention can be formed into any shape suitable for use as a cushioning device, for example for insertion into footwear to prevent rubbing between sensitive skin and hard or exposed surfaces of the footwear. The cushioning elements can also be applied to other garments (e.g., hats, helmets, protective sporting gear such as elbow and knee pads and other garments requiring extra padding for comfort, sizing and/or safety). Cushioning elements according to the invention may also be applied to surfaces which come in contact with body parts to provide protection from injury (e.g., chairs, desks, cabinets, tables, doors and door frames, among others). Depending on the size and shape of the object to which the cushioning element is applied, certain shapes will better protect different areas of the body from contact with the object. In certain example embodiments, the products are molded in the shape of circles, parabolas, stars, squares, rectangles, rounded rectangles, half-moon, among others. The appropriate shape of the cushioning element can be determined based on the size and surface of the object to which the cushioning element will be applied. In alternative example embodiments, the cushioning element can be provided as a sheet of material that the user can cut to a desired shape. The sheet of material can also be provided with preformed shapes that can be removed as desired for the appropriate protection from contact with the object.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications that are within the spirit and scope of the invention, as defined by the appended claims.
The cushioning device of the present invention in accordance with the embodiment depicted in
Unexpectedly, the probe tack of the cushioning device employing a multi-layer film was much higher than that of the single-layer linear low density polyethylene single-layer film. Further, following a 3-month accelerated aging period during which the cushioning devices were incubated in a 50° C. oven, the probe tack of the pressure sensitive adhesive of the cushioning device was much better retained in the multi-layer film as compared to the single-layer film. In fact, whereas the probe tack in the cushioning device of the multi-layer film was maintained at a desirable level, that of the single-layer film was insufficient for applications such as for use in a heel cushioning device.
The film surface friction was assayed in cushioning devices of the present invention in accordance with the embodiments depicted in
The lower the film surface friction, the better the rubbing relief. Accordingly, cushioning devices having a layer of MAH-LLDPE as the skin/sock-contact layer provide much better rubbing relief than those having a layer of TPU as the skin/sock-contact layer. Further, the low level of friction coefficient of the film surface achieved by a layer of MAH-LLDPE could not be achieved by a single layer of TPU film.
The bonding strength was assayed in a film material having a layer containing Lotader® 3210 (available from Arkema, Colombes, France) and a TPU layer. In particular, the film material had a layer of Lotader® 3210 with a thickness of 0.04 mm and a layer of TPU with a thickness of 0.14 mm. The bonding strength was assayed in accordance with (ASTM D 3807). The bonding strength between the layers of the film material was so strong that the layers could not be delaminated from each other. Such bonding strength may provide a more durable film material in applications associated therewith. In comparison, the typical bonding strength between a layer of MAH-LLDPE and a TPU layer is about 1.5 lb/in which is sufficient for applications associated with cushioning devices. Comparable delamination strength would be expected between a layer of other terpolymers having ethylene, butyl acrylate, butyl acetate or ethyl acetate, and MAH and a TPU layer.
The present application claims priority from U.S. Provisional Application Ser. No. 61/757,901, filed on Jan. 29, 2013, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61757901 | Jan 2013 | US |
