WO2018013553A1

WO2018013553A1 - Impact-absorbing material and assembly comprising the same and method for their manufacture

Info

Publication number: WO2018013553A1
Application number: PCT/US2017/041517
Authority: WO
Inventors: Sharon SOONG
Original assignee: Rogers Corporation
Priority date: 2016-07-14
Filing date: 2017-07-11
Publication date: 2018-01-18

Abstract

An impact-absorbing material that is capable of use for protecting an electronic device and that is formed from a miscible blend, in organic solvent, of a composition comprising more than 70 wt.% of a first component consisting of thermosetting silicone and less than 10 wt.% of a second component consisting of thermoplastic elastomeric block copolymer, wherein each weight percent is based on the total weight of Component A and Component B in the composition. Also disclosed is a method of manufacturing such impact-absorbing materials and an assembly that comprises the same in association with an electronic device.

Description

IMP ACT- ABSORBING MATERIAL AND ASSEMBLY COMPRISING THE SAME AND

METHOD FOR THEIR MANUFACTURE

FIELD

[0001] Disclosed herein are materials capable of providing effective impact protection and other benefits in cooperation with electronic devices or parts thereof. Such materials can be applied to an electronic device such as a mobile phone to absorb impact, seal the device, or otherwise insulate the device from external sources of harmful effects.

BACKGROUND

[0002] Electronic devices such as mobile phones, hard-disk drives, televisions, and liquid crystal displays typically consist of precise mechanical and electrical parts that require protection. Such electronic devices can be vulnerable, for example, to being damaged by an external source of impact. Furthermore, foreign pollutants such as dust can cause

overheating of an electronic device by disturbing the flow of air into an electronic device. Finally, electromagnetic waves from external sources can adversely affect the properties of electronic devices

[0003] In order to prevent such problems, an electronic device or parts thereof can be protected by a covering of material that absorbs external impacts and/or blocking the entry of undesirable pollutants into the device. Such materials can also be designed to absorb electromagnetic waves. For example, a compressible or elastic pad can be attached to an electronic device by using adhesive tape or by coating one face of the pad with adhesive.

[0004] Novel materials for providing impact protection for electronic devices have been developed. For example, WO 2010/016651 (UTIS) mentions a silicon pad for absorbing impact to electronic devices, although claiming a polyurethane pad. US

2009/0087608 discloses a roll-type composite sheet comprising a silicone gel for its impact- absorbing properties. The composition comprises an Fe-Si ferrite powder or the like for electromagnetic wave-absorbing properties. Toluene, methysiloxane, or naptha solvent is used to make the reaction product.

[0005] The prior art also discloses the mixture of silicone with other polymers to produce desirable properties. US Patent Publication 2014/0011898 discloses a composition comprising a thermoplastic elastomer, preferably a highly hydrogenated copolymer such as Kraton® SEBS(styrene-ethylene-butylene-styrene), and only a small amount of silicone in order to produce a silky feel for a cover on handheld electronics. The mixing of components is in an extruder to melt the polymers.

[0006] US Patent Publication 2012/0121876 discloses an elastomeric material for the absorption of impact energy that comprises a mixture of a thermoplastic elastomer having a specified Shore A hardness and a crosslinked silicone polymer. Styrenic triblock copolymers are preferred, including SBS (paragraph 0024). The examples use at most 40 weight percent silicone in combination with SEPS block copolymer, in a range of 15 to 40%, although the reference broadly mentions an amount of 5 to 70% by weight silicone. A list of possible applications includes a case for a cell phone (paragraph 0082). Crosslinking of the silicone takes place during hot mixing in a process referred to as dynamic vulcanization using plastic pellets. A sheet used for impact protection can be foamed or unfoamed (paragraph 0072 US Patent 6,013,715 discloses a method of preparing a composition, comprising a mixture of a thermoplastic (not an elastomer) and a siloxane, uses dynamic vulcanization. Similar patents are US 6,649,704 (with polyamide) and US 6,281,286 (with polycarbonate or poly(butylene terephthalate), or polyamide).

[0007] Despite the variety of materials and designs proposed for impact protection, as exemplified by the foregoing, it is apparent that there is a continuing need by electronics manufacturers for new and improved materials for such use. In particular, there remains a need for an impact-absorbing and/or sealing material for application to an electronic device in order to more effectively provide protection from adverse environmental influences. Thus, further improvements in the properties of impact-absorbing materials are desired. It would be desirable that impact absorbing material for an electronic device have improved toughness or tensile strength in addition to a combination of other desirable properties. It is desirable that such materials be capable of being applied to light, slim, and compact electronic devices. Finally, the materials must be capable of being readily manufactured.

SUMMARY

[0008] The present invention relates to an impact-absorbing material adaptable for use with an electronic device. An impact-protection assembly can comprise such a material, a surface of which is in contact with, or attached to, an inner or outer surface of an electronic device. In some embodiments, the impact-absorbing material at least partially encases the outer surface of a handheld electronic device such as a mobile phone.

[0009] In particular, some embodiments of the invention are directed to an impact- absorbing material capable of use for protecting an electronic device that is formed from a miscible blend, in organic solvent, of a composition comprising: more than 70 wt.% of Component A consisting of thermosetting silicone, and between 0.1 wt.% and 10 wt.% of Component B consisting of thermoplastic elastomeric block copolymer, wherein each of said weight percent is based on the total weight of Component A and Component B in the composition and wherein the combined weight of Component A and Component B comprises 80 to 100 weight percent of the total composition.

[0010] Other embodiments of the present invention are directed to an impact- absorbing material that is capable of use for protecting an electronic device and that is formed from a miscible blend, in organic solvent, of a composition comprising more than 70 wt.% of Component A consisting of thermosetting silicone; and between 0.1 wt.% to and 10 wt.% of Component B consisting of thermoplastic elastomeric block copolymer comprising styrene and butadiene blocks, wherein each weight percent is based on the weight of Component A and Component B in the composition and wherein the combined weight of Component A and Component B comprises 80 to 100 percent of the total composition, and wherein the material has a maximum thickness of 0.1 to 25 mm, and a tensile strength of greater than 120 psi.

[0011] Another aspect of the present invention is directed to a method of preparing an impact-absorbing material in sheet form (i.e., flattened in the x-y plane) by providing a thermosetting silicone composition (Component A) comprising a mixture of reactive parts, providing a thermoplastic elastomeric block copolymer (Component B), blending Component A and Component B employing an organic solvent that dissolves both Component A and Component B to obtain a miscible polymeric blend comprising more than 70 wt.% of Component A and between 0.1 and 10 wt.% of Component B consisting of thermoplastic elastomeric block copolymer, wherein each of said weight percents is based on the total weight of Component A and Component B in the composition, and wherein the combined weight of Component A and Component B comprises 80 to 100 weight percent of the total composition. The polymeric blend is heated at an elevated temperature to cure the thermosetting silicone composition, and the impact-absorbing material is formed by coating or casting a layer of the polymeric blend onto a substrate.

[0012] Still other embodiments of the invention are directed to an article comprising an electronic handheld device at least partially covered by a layer of an impact-absorbing material as described above.

[0013] The above described and other features are exemplified by the following figures and detailed description. DETAILED DESCRIPTION

[0014] An impact-absorbing material can be formed from a miscible polymeric blend as hereafter described. Subsequently, the impact-absorbing material can be attached to an electronic device, thereby absorbing or dispersing external impacts and preventing the influx of foreign pollutants.

[0015] A sheet of the material can be formed by casting, extrusion, molding, or other conventional process. In one embodiment, slot die casting is used to form the impact- absorbing material for use in association with an electronic device. Other methods for preparing the impact-absorbing material will be readily apparent to those skilled in the art.

[0016] The surface of the impact-absorbing sheet material can be substantially or generally planar, multi-planar, curved, or complex curved, indented, or otherwise shaped. For many applications, the thickness of the sheet material can be between about 0.1 mm and 25 mm, specifically 0.25 to 15 mm or 10 to 1000 mils (0.254 to 25.4 mm), and typically will be relatively small compared to the lengthwise or widthwise dimensions of the sheet material as defined along the x- and y-axes.

[0017] Since the material is, to some extent, compressible, it can also conform to the surfaces of an electronic device whether such surfaces are regular or somewhat irregular in shape. Thus, a sheet or pad of the material can provide impact protection for a variety of electronic devices and components thereof having impact-sensitive elements that otherwise may be vulnerable to damage that can reduce performance or that can even cause system failure.

[0018] The impact-absorbing material can exhibit a desirable combination of properties, including a tensile strength of greater than 120 psi, specifically 120 to 300 psi, more specifically 150 to 250 psi.

[0019] The impact-absorbing material can be formed from a solvent-blended composition comprising a miscible blend of more than 70 wt.%, specifically 70 to 99 wt.%, more specifically 72 to 92 weight percent, of thermosetting silicone polymer (which can be in reactive or non-reactive parts) and between 0.1 and 10 wt.%, specifically 1 to 9.9 wt.%, more specifically 2 to 9 wt.%, of a thermoplastic elastomeric block copolymer, wherein each weight percent is based on the total weight of Component A and Component B in the composition and wherein the total weight of Component A and Component B comprises 80 to 100 weight percent of the total composition, specifically 90 to 100 wt.% of the total composition (and more specifically 95 to 100 wt.% of the total polymer). Optional additives can be included as described below. [0020] Exemplary thermoplastic elastomeric block copolymers can comprise a block (A) derived from an alkenyl aromatic compound having 8 to 16, specifically 8 to 12 carbon atoms, and a block (B) derived from a conjugated diene. The thermoplastic elastomeric block copolymer can comprise substituted or unsubstituted styrene and butadiene blocks. Block copolymers can include, for example, styrene-butadiene diblock copolymer (SB), styrene- butadiene-styrene triblock copolymer (SBS), styrene-isoprene diblock copolymer (SI), styrene-isoprene-styrene triblock copolymer (SIS), styrene-(ethylene-butylene)-styrene triblock copolymer (SEBS), styrene-(ethylene-propylene)-styrene triblock copolymer (SEPS), and styrene-(ethylene-butylene) diblock copolymer (SEB).

[0021] Such polymers are commercially available, for example, from Shell Chemical Corporation under the trade names KRATON D-1101, KRATON D-1102, KRATON D- 1107, KRATON D-1111, KRATON D-1116, KRATON D-1117, KRATON D-1118, KRATON D-1119, KRATON D-1122, KRATON D-1135X, KRATON D-1 184, KRATON D-1144X, KRATON D-1300X, KRATON D-4141, KRATON D-4158, KRATON G1726, and KRATON G-1652. For example, KRATON D-1118 is a solid SB-SBS copolymer. This copolymer has polystyrene end blocks and a rubbery polybutadiene mid-block with about 20% SBS triblock and about 80% SB diblock. Thus, KRATON D-1118 is a mixed diblock/triblock styrene and butadiene copolymer, containing 30 volume% styrene. It is a low modulus, low cohesive strength, soft rubber.

[0022] The block copolymer can comprises a polybutadiene or polyisoprene block that is hydrogenated, thereby forming a polyethylene block (in the case of polybutadiene) or an ethylene -propylene copolymer (in the case of polyisoprene). An exemplary block copolymer of this kind is KRATON GX1855, which is believed to be a mixture of a styrene- high 1,2-butadiene-styrene block copolymer and a styrene-(ethylene-propylene)-styrene block copolymer.

[0023] The thermosetting silicone polymer can be obtained by reaction of a two-part heat-cured silicone composition. As will be appreciated by the skilled artisan, the heat-cured silicone composition can comprise a two-part LSR (liquid silicone rubber) or gel, or mixtures thereof, designed to obtain the desired properties for a particular application.

[0024] The impact-absorbing material can be formed from a total composition comprising, as precursor composition, a liquid silicone polymer (LSR), specifically comprising a polysiloxane having at least two alkenyl groups per molecule and a

polysiloxane having at least two silicon-bonded hydrogen atoms, in a quantity effective to cure the composition, further in the presence of a catalyst. Suitable reactive silicone compositions are low durometer, two-package (for example, 1 : 1) liquid silicone rubber (LSR) or liquid injection molded (LIM) compositions. Because of their low inherent viscosity, the use of a low durometer LSR or LIM composition can facilitate the addition of optional filler.

[0025] In one embodiment, an LSR or LIM system can be provided as a two-part formulation suitable for mixing in ratios of about 1 : 1 by volume. The "First Part" of the formulation can comprise one or more polysiloxanes having two or more alkenyl groups. Suitable alkenyl groups are exemplified by vinyl, allyl, butenyl, pentenyl, hexenyl, and heptenyl, specifically vinyl. The alkenyl group can be bonded at the molecular chain terminals, in pendant positions on the molecular chain, or both. Other silicon-bonded organic groups in the polysiloxane having two or more alkenyl groups can be exemplified by substituted and unsubstituted monovalent hydrocarbon groups, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; aryl groups such as phenyl, tolyl, and xylyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups such as 3- chloropropyl and 3,3,3-trifluoropropyl. Exemplary substituents are methyl and phenyl groups.

[0026] The alkenyl-containing polysiloxane can have straight chain, partially branched straight chain, branched-chain, or network molecule structure, or can be a mixture of two or more selections from polysiloxanes with the exemplified molecular structures. The alkenyl-containing polysiloxane is exemplified by trimethylsiloxy-endblocked

dimethylsiloxane-methylvinylsiloxane copolymers, trimethylsiloxy-endblocked

methylvinylsiloxane-methylphenylsiloxane copolymers, trimethylsiloxy-end blocked dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers,

dimethylvinylsiloxy-endblocked dimethylpolysiloxanes, dimethylvinylsiloxy-endblocked methylvinylpolysiloxanes, dimethylvinylsiloxy-endblocked methylvinylphenylsiloxanes, dimethylvinylsiloxy-endblocked dimethylvinylsiloxane-methylvinylsiloxane copolymers, dimethylvinylsiloxy-endblocked dimethylsiloxane-methylphenylsiloxane copolymers, dimethylvinylsiloxy-endblocked dimethylsiloxane-diphenylsiloxane copolymers,

polysiloxane comprising R3 S1O1/2 and S1O4/2 units, polysiloxane comprising RS1O3/2 units, polysiloxane comprising the R2S1O2/2 and RS1O3/2 units, polysiloxane comprising the

R2S1O2/2, RS1O3/2 and S1O4/2 units, and a mixture of two or more of the preceding

polysiloxanes. R represents substituted and unsubstituted monovalent hydrocarbon groups, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; aryl groups such as phenyl, tolyl, and xylyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups such as 3-chloropropyl and 3,3,3-trifluoropropyl, with the proviso that at least 2 of the R groups per molecule are alkenyl.

[0027] A "Second Part" of an LSR or LEVI system can comprise one or more polysiloxanes that contain at least two silicon-bonded hydrogen atoms per molecule and has an extrusion rate of less than about 500 g/minute. The hydrogen can be bonded at the molecular chain terminals, in pendant positions on the molecular chain, or both. Other silicon-bonded groups are organic groups exemplified by non-alkenyl, substituted and unsubstituted monovalent hydrocarbon groups, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; aryl groups such as phenyl, tolyl, and xylyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups such as 3-chloropropyl and 3,3,3-trifluoropropyl. Exemplary substituents are methyl and phenyl groups.

[0028] The hydrogen-containing polysiloxane component can have straight-chain, partially branched straight-chain, branched-chain, cyclic, network molecular structure, or can be a mixture of two or more selections from polysiloxanes with the exemplified molecular structures. The hydrogen-containing polysiloxane is exemplified by trimethylsiloxy- endblocked methylhydrogenpolysiloxanes, trimethylsiloxy-endblocked dimethylsiloxane- methylhydrogensiloxane copolymers, trimethylsiloxy-endblocked methylhydrogensiloxane- methylphenylsiloxane copolymers, trimethylsiloxy-endblocked dimethylsiloxane- methylhydrogensiloxane-methylphenylsiloxane copolymers, dimethylhydrogensiloxy- endblocked dimethylpolysiloxanes, dimethylhydrogensiloxy-endblocked

methylhydrogenpolysiloxanes, dimethylhydrogensiloxy-endblocked dimethylsiloxanes- methylhydrogensiloxane copolymers, dimethylhydrogensiloxy-endblocked dimethylsiloxane- methylphenylsiloxane copolymers, and dimethylhydrogensiloxy-endblocked

methylphenylpolysiloxanes.

[0029] The hydrogen-containing polysiloxane component is added in an amount sufficient to cure the composition, specifically in a quantity of about 0.5 to about 10 silicon- bonded hydrogen atoms per alkenyl group in the alkenyl-containing polysiloxane.

[0030] The silicone composition further comprises, generally with the "First Part," a catalyst such as platinum to accelerate the cure. Platinum and platinum compounds known as hydrosilylation-reaction catalysts can be used, for example platinum black, platinum-on- alumina powder, platinum-on-silica powder, platinum-on-carbon powder, chloroplatinic acid, alcohol solutions of chloroplatinic acid platinum-olefin complexes, platinum-alkenylsiloxane complexes and the catalysts afforded by the microparticulation of the dispersion of a platinum addition-reaction catalyst, as described above, in a thermoplastic resin such as methyl methacrylate, polycarbonate, polystyrene, silicone, and the like. Mixtures of catalysts can also be used. A quantity of catalyst effective to cure the present composition is generally from 0.1 to 1,000 parts per million (by weight) of platinum metal based on the combined amounts of alkenyl and hydrogen components.

[0031] Reactive polysiloxane fluids co-cure with the alkenyl-containing polysiloxane and the polysiloxane having at least two silicon-bonded hydrogen atoms, and therefore can themselves contain alkenyl groups or silicon-bonded hydrogen groups. Such compounds can have the same structures as described above in connection with the alkenyl-containing polysiloxane and the polysiloxane having at least two silicon-bonded hydrogen atoms, but in addition have a viscosity of less than or equal to about 1000 centipoise (cps), specifically less than or equal to about 750 cps, more specifically less than or equal to about 600 cps, and most specifically less than or equal to about 500 cps. In one embodiment, the reactive polysiloxane fluids have a boiling point greater than the curing temperature of the addition cure reaction.

[0032] The Component A of the impact-absorbing material can further optionally comprise a curable silicone gel formulation. Silicone gels are lightly cross-linked fluids or under-cured elastomers. They are unique in that they range from very soft and tacky to moderately soft and only slightly sticky to the touch. Use of a gel formulation decreases the viscosity of the composition, thereby allowing (with optional filler) at least one of an increased filler loading, enhanced filler wetting, and/or enhanced filler distribution. Thus, some embodiments can provide cured compositions having lower resistance and resistivity values and increased softness. Suitable gel formulations can be either two-part curable formulations or one-part formulations. The components of the two-part curable gel formulations is similar to that described above for LSR systems (i.e., an organopolysiloxane having at least two alkenyl groups per molecule and an organopolysiloxane having at least two silicon-bonded hydrogen atoms per molecule). The main difference lies in the fact that the molar ratio of the silicon-bonded hydrogen groups (Si-H) groups to the alkenyl groups is usually less than one, and can be varied to create a "under-cross linked" polymer with the looseness and softness of a cured gel. Specifically, the ratio of silicone-bonded hydrogen atoms to alkenyl groups is less than or equal to about 1.0, specifically less than or equal to about 0.75, more specifically less than or equal to about 0.6, and most specifically less than or equal to about 0.1. An example of a suitable two-part silicone gel formulation is

SYLGARD® 527 gel commercially available from the Dow Corning Corporation. [0033] Optionally, a low viscosity reactive or non-reactive polysiloxane fluid having a viscosity of about 100 to about 1000 centipoise can also be present. A non-reactive silicone fluid can thus become part of the polymer matrix, leading to low outgassing and little or no migration to the surface during use. In one embodiment, the boiling point of the non-reactive polysiloxane fluid can be high enough such that when it is dispersed in the polymer matrix, it does not evaporate during or after cure, and does not migrate to the surface or outgas. Use of the low viscosity polysiloxane fluid can obviate the need for an organic solvent and a subsequent removal step.

[0034] The composition for forming the impact-absorbing material can optionally comprise filler particles, which particles become homogenously dispersed in a polymer matrix in the final composite product. Generally the loading can be in an amount of from about 1% to about 25% by weight of the material. The particles can be incorporated into the silicone Component A, using any number of conventional techniques well known in the art, such as by compounding, blending, or the like. In this regard, the filler particles can be of any particulate shape, including solid or hollow, spherical or microspherical, flakes, platelets, irregularly shaped particles, or fibers. A powder can be used for obtaining uniform dispersal and homogeneous mechanical and other properties. The particle size or distribution of the filler typically can range from between about 0.01 mil to about 10 mil, specifically 10 to 500 micrometers (μπι), which refers to mean diameter or equivalent diameter as determined by standard laser particle measurement. Particulate fillers can include metal/non-metal oxides, nitrides, carbides, borides, graphite, and metal particles, and mixtures thereof, for example, metal oxides such as aluminum oxide, magnesium oxide, zinc oxide, beryllium oxide, and antimony oxide. Optional fillers that can provide improved thermal conductivity can include, for example, boron nitride (BN), titanium diboride, aluminum nitride, silicon carbide, and graphite, and mixtures thereof.

[0035] In addition to the above-mentioned optional fillers in the formulation of the impact-absorbing material, and depending upon the requirements of the particular application envisioned, other optional filler additives can be added to the reactive composition, e.g., alumina trihydrate, silica, talc, calcium carbonate, clay, and so forth; pigments (for example titanium dioxide and iron oxide), and so forth. Reinforcing fillers such as woven webs and glass particles or glass microballoons can be included if desired.

[0036] In addition to optional fillers, other additives known for use in the

manufacture of sheet materials can be present in the composition for forming the impact- absorbing material. Suitable flame retardants include, for example, metal hydroxides containing aluminum, magnesium, zinc, boron, calcium, nickel, cobalt, tin, molybdenum, copper, iron, titanium, or a combination thereof, for example, aluminum trihydroxide, magnesium hydroxide, calcium hydroxide, iron hydroxide, and the like; and brominated compounds. Exemplary flame retardant materials are magnesium hydroxides, nanoclays, and brominated compounds. In one embodiment, flame resistance of the impact-absorbing material meets certain Underwriter's Laboratories (UL) standards for flame retardance, for example, a rating of V-0 under UL Standard 94.

[0037] Still other additives that can be present include dyes, antioxidants, ultraviolet (UV) stabilizers, catalysts for cure of the polymer, crosslinking agents, and the like, as well as combinations comprising at least one of the foregoing additives.

[0038] In another aspect of the invention, the impact-absorbing sheet material can be prepared by a method comprising providing a thermoset silicone polymeric composition, referred to as Component A, providing a thermoplastic elastomeric block copolymer component, referred to as Component B; blending Component A and Component B employing an organic solvent that dissolves both Component A and Component B in the solvent to obtain a miscible polymeric blend; heating the miscible polymeric blend at an elevated temperature to cure the thermosetting silicone polymeric composition; and forming an impact-absorbing material by coating or casting the polymeric blend onto a substrate and removing solvent, wherein the polymeric blend comprises more than 70 wt.% of Component A and less than 10 wt.% of Component B, wherein each weight percent is based on the total weight of Component A and Component B in the composition and wherein the combined weight of Component A and Component B comprises 80 to 100 weight percent of the total composition.

[0039] After the impact-absorbing material is shaped, for example, using die slot casting onto a temporary carrier, and then at least partially cured. The material can be cured in an oven at an elevated temperature for an appropriate time, for example 1 minute to 60 minutes and optionally can be passed to a cooling zone where it is cooled by any suitable cooling device such as a fan. Where appropriate, after then solvent is removed, the impact- absorbing material can be taken up on a roll for later use. In such a production mode, the length of the sheet material can be up to 5 meters or more.

[0040] Still another aspect of the invention relates to an article, or assembly comprising an electronic handheld/mobile device at least partially covered by the above- described impact-absorbing sheet material in direct or indirect contact (for example, via an adhesive layer) with a surface of the device. The dimensions of the impact-absorbing material can be changed depending on the particular application. In some embodiments, a thickness of 0.1 mm to 2.0 mm is used. Within the above range, it can provide the minimum amount of impact absorption and sealing effect on an uneven surface of an electronic device. In view of the improved properties, relatively thinner materials can be used to provide the desired level of protection, thereby allowing an encased electronic device to become lighter, thinner, or smaller.

[0041] Applications within the scope of the present invention can include, by way of example, consumer electronics such as cell phones, computer monitors, TVs, automotive electronic components and systems, and the like. It will be appreciated that aspects of the present invention can find advantageous use in various other applications requiring a resilient sheet material.

[0042] The properties of the impact-absorbing material (e.g., density, modulus, compression load deflection, tensile strength, tear strength, and so forth) can be adjusted by varying the amounts of the components of the reactive compositions. For example, a sheet material can have a compression set resistance of less than or equal to about 10%, specifically 1%) to 10%), more specifically less than or equal to about 5%, after 50%> compression for 22 hours at room temperature; and a compression force deflection at 25% of 1 to 20 psi, specifically 2 to 15 psi, so that the material can have the capacity to absorb impact and to seal an electronic device for a long time.

[0043] Modulus as reflected by compression force deflection (CFD) can be determined on an Instron® instrument. CFD can be measured by calculating the force in pounds per square inch (psi) required to compress the sample to 25% of the original thickness in accordance with ASTM D1056.

[0044] In some embodiments, the tensile strength of the material can range from 4 can be 2 to 10 kgf/cm². Also, in some embodiments, the tensile elongation of the material ranges from 100 to 300% so as to be able to closely or securely attach the material to the an electronic device. With the addition of optional thermally conductive filler, the impact- absorbing material can have a thermal conductivity of about 0.2 W/m-K or greater if desired.

EXAMPLES

[0045] Testing: Tensile strength and elongation are measured using an Instron® instrument fitted with a 20 kilogram (50-pound) load cell and using 4.5-9.0 kilogram range depending on thickness and density. Tensile strength is calculated as the amount of force in kilogram per square centimeter (kg/cm²) at the break divided by the sample thickness and multiplied by two. Elongation is reported as percent extension. To test the impact-absorbing materials, a standard mass impact test was employed in which a steel ball having a mass of 4.3 grams was dropped from a height of 30.5 centimeters about the sample material. The impact force was recorded and compared to the impact force measured without the impact- absorbing material present to provide the force reduction as a percent.

[0046] An impact-absorbing sheet material was prepared as follows. The materials used in the Examples are shown in Table 1.

Table 1

[0047] The Silicone Component A used in the experimental formulations included a composition that was a combination of (Sub-Component 1) Dow Corning Sylgard® 527, which is a two-part heat-cured soft gel with low viscosity and (Sub-Component 2)

Momentive LIM 6040®, which is a two-part heat-cured LSR to provide toughness.

[0048] Two formulation examples (Control and Inventive) are shown in Table 2 below.

Table 2

[0049] Sample Preparation: The parts of each silicone (two-part) formulation were first mixed separately using a high speed mixer (Flacktec®) until both were homogeneous. Silicone formulation 1 (60 g) and silicone formulation 2 (40 g) were then mixed together using the same mixer to form a silicone base composition.

[0050] The elastomeric block copolymer (30 g) was dissolved in 100 of the toluene solvent. The copolymer/toluene mixture (21.7 g) was added to 100 g of the silicone base composition to make a block-elastomer-modified silicone composition (5 wt.% solids), wherein the solvent had been selected to provide a miscible polymeric blend.

[0051] The modified silicone composition formed a uniform thermoplastic/thermoset hybrid film. No phase separation was observed. The film was tested and the test results are shown in Table 3 below.

Table 3

[0052] Based on the results in Table 3, impact-absorbing sheet sheets according to the present invention were shown to exhibit significantly increased toughness while maintaining satisfactory elongation.

[0053] Ranges disclosed herein are inclusive of the recited endpoint and combinable (e.g., ranges of "up to about 25 wt.%, or, more specifically, about 5 wt.% to about 20 wt.%", is inclusive of the endpoints and all intermediate values of the ranges of "about 5 wt.% to about 25 wt.%)," etc.). "Combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. Also, "combinations comprising at least one of the foregoing" clarifies that the list is inclusive of each element individually, as well as combinations of two or more elements of the list, and combinations of one or more elements of the list with non- list elements. Furthermore, the terms "first," "second," and so forth, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier "about" used in connection with a quantity is inclusive of the state value and has the meaning dictated by context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix "(s)" as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the foam(s) includes one or more foams). Reference throughout the specification to "one embodiment", "another embodiment", "an embodiment", and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and is optionally present in other embodiments. In addition, it is to be understood that the described elements can be combined in any suitable manner in the various embodiments. As used herein, the terms sheet, film, plate, and layer, are used interchangeably, and are not intended to denote size.

[0054] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0055] While the invention has been described with reference to several embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

What is claimed is:

1. An impact-absorbing material that is capable of use for protecting an electronic device and that is formed from a miscible blend, in organic solvent, of a composition comprising:

more than 70 weight percent of Component A consisting of thermosetting silicone; and

between 0.1 and 10 weight percent of Component B consisting of thermoplastic elastomeric block copolymer;

wherein each of said weight percents is based on the total weight of Component A and Component B in the composition and wherein the combined weight of Component A and Component B comprises 80 to 100 percent of the total composition.

2. The impact-absorbing material of claim 1 wherein the material exhibits a tensile strength of 120 to 300 psi.

3. The impact-absorbing material of claim 1 wherein the thermoplastic elastomeric block copolymer comprising units derived from an alkenyl aromatic compound and a conjugated diene.

4. The impact-absorbing material of claim 3 wherein the alkenyl aromatic compound is styrene and the conjugated diene is polybutadiene.

5. The impact-absorbing material of claim 1 wherein the thermosetting silicone is a two-part heat cured silicone composition.

6. The impact-absorbing material of claim 5 wherein the heat cured silicone comprises a two-part LSR (liquid silicone rubber) or gel.

7. The impact-absorbing material of claim 1 wherein the elastomeric block copolymer is selected from the group consisting of styrene-butadiene diblock copolymers, styrene-butadiene-styrene triblock copolymers, styrene-isoprene diblock copolymers, styrene- isoprene-styrene triblock copolymers, styrene-(ethylene-butylene)-styrene triblock copolymers, styrene-(ethylene-propylene)-styrene triblock copolymers, styrene-(ethylene- butylene) diblock copolymers, and combinations comprising at least one of the foregoing copolymers.

8. The impact-absorbing material of claim 1 wherein the block copolymer is a styrene-butadiene diblock copolymer, styrene-butadiene-styrene triblock copolymer, or a combination comprising at least one of the foregoing copolymers.

9. An impact-absorbing material that is capable of use for protecting an electronic device and that is formed from a miscible blend, in organic solvent, of a composition comprising:

between 0.1 and 10 weight percent of Component B consisting of thermoplastic elastomeric block copolymer comprising styrene and butadiene blocks;

wherein each of said weight percents is based on the total weight of Component A and Component B in the composition and wherein the combined weight of Component A and Component B comprises 80 to 100 weight percent of the total composition;

wherein the material has a maximum thickness of 0.1 to 25 mm and a tensile strength of greater than 120 psi.

10. A method of preparing an impact-absorbing sheet for use with a handheld device comprising:

providing a thermosetting silicone composition, Component A, comprising a mixture of reactive parts;

providing a thermoplastic elastomeric block copolymer component, Component B; blending Component A and Component B employing an organic solvent that dissolves both Component A and Component B to obtain a miscible polymeric blend comprising more than 70 wt.% of Component A and less than 10 wt.% of Component B consisting of thermoplastic elastomeric block copolymer, wherein each of said weight percents is based on the total weight of Component A and Component B in the composition and wherein the combined weight of Component A and Component B comprises 80 to 100 weight percent of the total composition; heating the polymeric blend at an elevated temperature to cure the thermosetting silicone composition; and

forming an impact-absorbing material by coating or casting a layer of the polymeric blend onto a substrate.

11. The method of claim 10, wherein slot-die casting is used to form a sheet of the impact-absorbing material.

12. An article comprising an electronic handheld device at least partially covered by a layer of the impact-absorbing material of claim 1.

13. The article of claim 12 wherein the handheld device is a mobile phone and wherein a surface of the impact-absorbing material is in contact with, or adhesively attached to, an outer surface of the electronic handheld device.

14. The impact-absorbing material of claim 1 wherein the material is in the shape of a sheet having an average thickness of 0.1 to 25 mm.

16. The impact-absorbing material of claim 1 wherein the compression force deflection of the material is 1 to 20 psi.

17. The impact-absorbing material of claim 1 wherein the material has a thickness of 0.1 to 25 mm and a compression force deflection of 2 to 12 psi.

18. The impact-absorbing material of claim 1, wherein a sheet of the material has a tensile strength of 2 to 10 kgf/cm².

19. The impact-absorbing material of claim 1, wherein a sheet of the material has a coefficient of extension of 100 to 300%.

20. The impact-absorbing material of claim 1, composition comprises 85 to 99 wt.% of Component A and 1 to 9 wt.% of Component B, based on total weight of polymer in the composition.