WO2006062833A1

WO2006062833A1 - Acoustic surfaces made from nanocomposites

Info

Publication number: WO2006062833A1
Application number: PCT/US2005/043714
Authority: WO
Inventors: David Jarus; John Schulz
Original assignee: Polyone Corporation
Priority date: 2004-12-07
Filing date: 2005-12-05
Publication date: 2006-06-15

Abstract

An acoustic surface is disclosed, made of a nanocomposite which contains a thermoplastic matrix and organoclay at least partially exfoliated therein. The acoustic surface is particularly suitable for an acoustic speaker, baffle, or enclosure. The organoclay contributes stiffness. Other optional ingredients include conventional essentially halogen-free flame retardants, intumescent essentially halogen-free flame retardants, and other typical polymer compounding additives.

Description

ACOUSTIC SURFACES MADE FROM NANOCOMPOSITES

CLAIM OF PRIORITY

[0001] This application claims priority from U.S. Provisional Patent

Application Serial Number 60/633,817 bearing Attorney Docket Number 12004014 and filed on December 7, 2004.

FIELD OF THE INVENTION

[0002] This invention relates to acoustic surfaces, such as speaker cones, made from thermoplastics having nanoclays dispersed therein.

BACKGROUND OF THE INVENTION

[0003] Nanoclays are exciting additives for a variety of purposes. U.S.

Pat. Nos. 6,376,591 ; 6,251,980; 6,232,388; 6,225,394; 6,090,734; 6,050,509; 5,998,528; 5,844,032; and 5,837,763 disclose the manufacture and use of nanocomposites, which are exfoliated nanoclays in a plastic matrix. Nanocor, Inc. is a significant commercial source of exfoliated or intercalated nanoclays and has a web site: www.nanocor.com. Also PolyOne Corporation (www.polyone.com) is a source of Nanoblend™ nanoclay concentrates for use in polyolefin compounds and Maxxam^® LST nanocomposite compounds. [0004] Acoustic surfaces need stiffness in order to control sound waves.

For example, speaker cones in acoustic loudspeakers for stereo equipment, automobile sound systems, etc. have struggled with the balance between acoustic enhancement to amplify the sound with avoiding reverberations and other acoustic defects.

[0005] As reported in the acoustic speaker industry, "the basic material parameters that affect the acoustic performance of a cone material are its density, stiffness, and internal lossiness (i.e., the internal damping). Very loosely speaking, the stiffer and lighter a cone material is, the wider the bandwidth of the cone will be. The more lossy it is, the smoother the response. Unfortunately, the above parameters are typically interactive, and it is very difficult to optimize all three parameters simultaneously." [0006] Consequently, speaker cones have been made using paper, cloth, carbon fiber matrix, polyolefins, and modifications of them using a variety of surface treatments. For sound systems that endure a wide variety of environments of temperature and humidity, such as motor vehicle speakers, degradable materials such as paper and cloth are not preferred. However, the balance of acoustic properties suffer.

SUMMARY OF THE INVENTION

[0007] What the art needs is a material that balances the acoustic properties required for acoustic surfaces, such as speaker cones, with durability for a variety of temperate, tropical, and frigid environments.

[0008] For purposes of this invention, "nanocomposite" means mixture comprising thermoplastic matrix polymer and organoclay (also known as intercalated nanoclay), whether to be used as a concentrate or as a compound.

The organoclay is dispersed (also known as exfoliated) throughout the thermoplastic matrix polymer, preferably as uniformly and minutely as possible.

However, complete exfoliation is not required. Optionally, but preferably to assist dispersion, the nanocomposite contains a compatibilizing dispersion agent, such as maleated polyolefin.

[0009] The present invention solves that problem in the art by using a nanocomposite to make the acoustic surface, preferably the speaker cone of a acoustic audio device.

[00010] One aspect of the present invention is a acoustic surface comprised of a nanocomposite, wherein the nanocomposite comprises a thermoplastic matrix and organoclay at least partially exfoliated therein. [00011] Another aspect of the present invention is an acoustic speaker having a acoustic surface described immediately above.

[00012] An advantage of the present invention is that the nanocomposite has lightness and stiffness required for acoustic performance and durability required for long-term usage in a variety of environments.

[00013] Additional features and advantages will be identified below.

EMBODIMENTS OF THE INVENTION [00014] Organoclav

[00015] Nanoclay is a clay from the smectite family. Smectites have a unique morphology, featuring one dimension in the nanometer range. Montmorillonite clay is thelmost common member of the smectite clay family. The montmorillonite clay particle is often called a platelet, meaning a sheet-like structure where the dimensions in two directions far exceed the particle's thickness.

[00016] Nanoclay becomes commercially significant if intercalated with an intercalant, to become an organoclay. An intercalate is a clay-chemical complex wherein the clay gallery spacing has increased, due to the process of surface modification by an intercalant. Under the proper conditions of temperature and shear, an intercalate is capable of exfoliating in a thermoplastic resin matrix. An intercalant is an organic or semi-organic chemical capable of entering the montmorillonite clay gallery and bonding to the surface. Exfoliation describes a dispersion of a surface treated nanoclay in a plastic matrix. In the present invention, the intercalated nanoclay (i.e., organoclay) is at least partially exfoliated in the thermoplastic matrix. [00017] In exfoliated form, nanoclay platelets have a flexible sheet-type structure which is remarkable for its very small size, especially the thickness of the sheet. The length and breadth of the particles range from 1.5 μm down to a few tenths of a micrometer. However, the thickness is astoundingly small, measuring only about a nanometer (a billionth of a meter). These dimensions result in extremely high average aspect ratios (200 - 500). Moreover, the miniscule size and thickness mean that a single gram contains over a million individual particles.

[00018] As stated above, nanocomposites are the combination of the surface treated nanoclay and the plastic matrix. In polymer compounding, a nanocomposite concentrate is a very convenient means of delivery of the nanoclay into the ultimate compound, provided that the plastic matrix is compatible with the principal polymer resin components of the compounds. Otherwise, the nanocomposite can have all ingredients associated with a polymer compound mixed therein.

[00019] In such manner, nanocomposites are available in concentrates, masterbatches, and compounds from Nanocor, Inc. of Arlington Heights, Illinois (www.nanocor.com) and PolyOne Corporation of Avon Lake, Ohio (www.polyone.com) in a variety of nanocomposites. For example, one preferred nanocomposite is Nanoblend™ Concentrate 1001 available from PolyOne Corporation. [00020] Thermoplastic Matrix

[00021] Any thermoplastic resin that is capable of achieving lightness and stiffness to achieve the acoustic performance required by the audio industry is suitable for use in this invention. More desirably, the thermoplastic resin is also a durable material in a variety of environments required for mass production of products without knowledge of ultimate product destination. Alternatively, if the specific environment is known for a specialized product, the choice of thermoplastic resin in terms of durability can be adjusted accordingly. Without undue experimentation, those skilled in the art of thermoplastic compounding can select a suitable thermoplastic resin to be the matrix for the nanocomposite.

[00022] Non-limiting examples of thermoplastic resins suitable for dispersing organoclays therein include polyolefins, polyhaloolefins, poly(meth)acrylates, polyamides, polyimides, polyesters, polycarbonates, and combinations thereof. Of these choices, polyolefins are preferred because of cost, availability, processing ease, and durability.

[00023] "Polyolefin" includes homopolymers, copolymers, blends of polymers, mixtures of polymers, alloys of polymers, and combinations thereof, where at least one of the polymers is polymerized from an olefin monomer having from 2 to about 8 carbon atoms.

[00024] Within the broad definition above, non-limiting examples of polyolefins suitable for the present invention include polyethylene (including low-density (LDPE), high-density, high molecular weight (HDPE), ultra-high molecular weight (UHDPE), linear-low-density (LLDPE), very-low density, etc.), maleated polypropylene, polypropylene, polybutylene, polyhexalene, polyoctene, and copolymers thereof, and mixtures, blends or alloys thereof. [00025] Particularly preferred is a blend of a polypropylene homopolymer or copolymer of propylene and ethylene, either one with a maleated polypropylene. The maleated polypropylene is capable of increasing dispersion of organoclay into the polyolefin and is commercially available from Crompton Corporation under the Polybond brand. [00026] Optionally for some acoustic surfaces, the polyolefin nanocomposite can have impact modifiers included therein. In the case of speaker cones needing stiffness and lightness, but not necessarily toughness, the addition of impact modifiers may not be needed or desired. The parameter of lossiness for a speaker cone, as explained above, needs to be included in the determination of an appropriate thermoplastic matrix.

[00027] Impact modifiers are typically elastomers such as natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, nitrile rubber, butyl rubber, ethylene-propylene-diene rubber (EPDM), ethylene-octene copolymers, and other elastomers. Minor amounts of impact modifiers can alter the impact strength according to preferences of those skilled in the art, to be determined without undue experimentation. For example, polybutadiene rubber, ethylene-propylene-diene rubber (EPDM), ethylene-octene copolymers, and other elastomers are useful. Non-limiting examples of such elastomers are those commercially available from multinational companies such as Bayer, Dupont-Dow Elastomers, Uniroyal Chemical, ExxonMobil, and others. ENGAGE™ 8180, ENGAGE™ 8842, and other ENGAGE™ polyolefin elastomers are especially preferred ethylene-octene copolymers available from DuPont Dow Elastomers LLC of Wilmington, DE that function well as impact modifiers for nanocomposites of the invention.

[00028] Commercially available polyolefin nanocomposites can be used in the acoustic surfaces of the present invention. A particularly preferred impact modified polyolefin nanocomposite is sold by PolyOne Corporation as Maxxam^® LST nanocomposite, wherein the LST is an acronym for light, stiff, and tough. A particularly preferred polyolefin nanocomposite without impact modifiers is Nanoblend™ Concentrate 1001 which contains a general purpose injection molding grade polypropylene nanocomposite. [00029] The weight percent of organoclay in the thermoplastic nanocomposite can range from about 0.5 to about 50 weight percent, and preferably from about 4 to about 15 weight percent. Preferably, the organoclay is from Nanocor, Inc. marketed under the Nanomer™ brand with product numbers I44P, DOP, and 124, depending on the type of intercalant used. [00030] Optional Flame Retardants

[00031] Optionally, flame retardants can be added to either or both nanocomposites of the present invention. Essentially halogen-free flame retardants are preferred because halogens are not emitted during combustion. [00032] Any conventional flame retardant that is essentially halogen-free is suitable for the present invention. Non-limiting examples of flame retardants include metal hydroxides, metal borates, antimony oxides, aryl phosphates, molybdate salts, ammonium polyphosphate, melamines, acid generating salts, silicones, and combinations thereof. Of these, aluminum tri-hydrate (ATH), magnesium hydroxide, and tri-tolyl phosphate are particularly preferred. [00033] The amount of optional conventional flame retardant can be added in an amount from 0 to about 50 weight percent, and preferably from 0 to about 30 weight percent of the total nanocomposite.

[00034] Intumescent flame retardants are also optional additives in the present invention. Providing intumescence to a polyolefin polymer typically requires, as explained in U.S. Pat. No. 6,632,442 (Chyall et al.), an acid source, a carbonific and spumific or nitrogen source component. These components may be in the same chemical compound. For example, ammonium polyphosphate will function as both an acid source and a nitrogen source as will be readily appreciated by one of skill in the art. Likewise, pentaerythritol phosphate alcohol (PEPA) functions as both an acid source and a carbonific. Melamine phosphate can provide carbon for the char, nitrogen for foaming and acid to catalyze dehydration and thus is a particularly preferred ingredient. [00035] In some embodiments, the acid source and nitrogen source are supplied in whole or in part by way of a single chemical compound selected from the group consisting of: ammonium phosphate, ammonium polyphosphate, ammonium pyrophosphate and mixtures thereof.

[00036] Flame retardant polymer compositions are those that foam and char to provide flame resistance, typically increasing in volume by more than 50 percent, preferably on the order of 100 percent based on the unreacted volume of the composition. The compositions thus typically include an acid catalyst source, a nitrogen source and a carbonific which may be the matrix polyolefin polymer itself or may be a polyol, or may be provided by way of a multifunctional ingredient such as pentaerythritol phosphate alcohol. [00037] Acid sources may be borates, sulfates, sulfites, nitrates, phosphates, phosphonates, melamine or other salts of the foregoing, and so forth.

[00038] Additional examples of flame retardant phosphorus-containing flame retardants include melamine salts of organophosphates such as melamine phenyl phosphate and melamine amyl phosphate. [00039] There are many commercially available sources of intumescent flame retardant materials, in any of the combinations described above. A preferred commercial source of flame retardant material is Amfϊne Chemical Corporation of Allendale, NJ, and particularly its Amfine FP 2000 brand nitrogen-phosphorous based flame retardant product. |00040] The amount of optional intumescent flame retardant can be added in an amount from 0 to about 40 weight percent, and preferably from 0 to about 30 weight percent of the total nanocomposite. [00041] Further, any metal salt of an organic sulfonic acid which provides flame retardant activity in a polyolefin can be used in the polyolefin nanocomposite. Examples of such cationic moieties of flame retardant compounds include alkali and alkaline earth metal salts such as sodium, potassium, calcium, barium and the like.

[00042] The organic moiety of the salt is generally an aromatic or perfluoro halogenated group with a sulfonic acid substituent. Examples of such organic moieties include perfluoro butyl sulfonic acid, perfluorooctyl sulfonic acid, benzene sulfonic acid, trichlorobenzene sulfonic acid, p-benzene sulfonyl benzene sulfonic acid and the like.

[00043] Examples of patents disclosing such salts include U.S. Pat. Nos.

3,933,734; 3,931,100; 3,948,851; 3,953,396; 3,926,908; 3,909,490; 3,919,167; and 4,066,618. Of these various metal salts of organic sulfonic acids, sodium trichlorobenzene sulfonate (STB) or potassium diphenyl sulfone sulfonate (KSS) is preferred. Of STB and KSS, KSS is preferred and is commercially available from Seal Sands Chemicals Ltd. of Middlesbrough, U.K. [00044] Any amount of flame retardant agent which is effective to flame retard polyolefin and which is sufficient to cause the observed severe melt degradation when employed in combination with organoclay is within the scope of the invention. The minimum amount of flame retardant in such compositions which experience the severe melt degradation is dependent upon the specific composition components employed. [00045] Other Optional Additives

[00046] As with any polymeric resin-based compound, optional additives can provide easier processing and more desirable final appearance and properties for the compound. The situation is no different for a nanocomposite suitable for use as a acoustic surface.

[00047] Non-limiting examples of optional additives include fibers, fillers, antioxidants, stabilizers, lubricants, pigments, biocides, and the like, and combinations thereof. None of these ingredients is essential to the performance of the nanocomposite. But each of them can provide added value to the final polymer blend when included for their intended purposes. Each of these additives is commercially available from well-known sources known to those skilled in the art.

[00048] For example, other fibers, synthetic or natural, such as carbon fiber, Kevlar® resin fiber and others can range from 0 to about 60, and preferably about 10 to 30 weight percent of the blend of the nanocomposites.

[00049] For example, impact modifiers can range from 0 to about 8, and preferably about 0.5 to 4 weight percent of the blend of the nanocomposites.

[00050] For example, mineral fillers can range from 0 to about 40, and preferably from about 2 to about 30 weight percent of the blend of the nanocomposites.

[00051] Antioxidants can range from 0 to about 1.0, and preferably from about 0.05 to about 0.3 weight percent of the blend of the nanocomposites.

[00052] Ultra-violet light stabilizers can range from 0 to about 5, and preferably from about 0.35 to about 3 weight percent of the blend of the nanocomposites.

[00053] Lubricants can range from 0 to about 2, and preferably from about 0.7 to about 1.5 weight percent of the blend of the nanocomposites.

[00054] Pigments can range from 0 to about 20, and preferably from about 2 to about 5 weight percent of the blend of the nanocomposites. [00055] Biocides can range from 0 to about 5, and preferably from about

0.5 to about 3 weight percent of the blend of the nanocomposites. [00056] Method of Processing Thermoplastic Nanocomposite

[00057] The preparation of polyolefin nanocomposites uses extrusion mixing equipment known to those skilled in the art, such as disclosed in U.S. Pat. No. 6,632,868 (Qian et al.) Two alternative means of processing are available.

[00058] In the first means, a concentrate is made by mixing thermoplastic resin and organoclay, and optionally a compatibilizing dispersion agent such as maleated polypropylene (PP-g-MAH).

[00059] In the second means, the constituents, thermoplastic resin and a polyolefin elastomer for impact modification are added separately and at different locations in the extruder. More specifically, the polyolefin elastomer is added downstream of the other ingredients, which gives the organoclay and its optional dispersion agent both more time and less interference in dispersing completely within the thermoplastic resin.

[00060] Preferably, the mixing equipment is a co-rotating twin-screw extruder commercially available from Werner-Pfleiderer. The extruder should be capable of screw speeds ranging from about 50 to about 2,000 rpm. The temperature profile from the barrel number two to the die should range from the melting temperature of the thermoplastic matrix polymer to about 270°C, and preferably from around 200°C for this nanoconcentrate. The nanocomposite can be pelletized for later use in the present invention. [00061] Method of Making Acoustic Surfaces

[00062] The acoustic surfaces of the present invention can be made using thermoplastic processing equipment known to those skilled in the art, such as conventional extrusion, molding, calendering, vacuum forming or other form- generating production equipment. The acoustic surfaces make take several forms, such as essentially two-dimensional sheets, three-dimensional articles, etc. The properties of the nanocomposite reside throughout the mass of the compound, whatever its form. Non-limiting examples of forms are films, profiles, articles, fibers, and the like. Articles can be then made into super structures such as laminates, foam cores or other suitable structures. Other methods include making a fiber of the nanocomposite and then a subsequent woven or non woven structure. Also, after the form is made, then subsequent techniques known to those skilled in the art can be employed, such as metallizing or foaming the polymeric acoustic surface.

[00063] Of various processing techniques, molding of three-dimensional articles is preferred, such as vacuum forming, compression molding and injection molding.

[00064] When using the nanocomposite in the form of a concentrate, generally the concentrate can be diluted or "let down" into the same thermoplastic resin or a compatible one thereto with little or no change to the processing method for molding the article from that thermoplastic. However, it is preferable when using injection molding and a nanocomposite concentrate such as Nanoblend™ Concentrate 1001 that the molding equipment be used with a low back pressure and low screw speed.

[00065] When using a nanocomposite compound, the mixing of ingredients need not occur at the article forming facility.

[00066] Actual refinements to the molding processing conditions are well within the skill of an ordinary person in the plastic molding industry.

USEFULNESS OF THE INVENTION

[00067] The acoustic industry relies as much on the art of sound as the physics of material science. Because acoustics fundamentally is the collision of sound waves and surfaces, the use of stiff materials to communicate desired sound are very much in need.

[00068] Non-limiting examples of acoustic surfaces are those which transfer sound waves from a point source (such as within the cone of a speaker) and those which reflect or deflect sound waves from a variety of potential sources (such as a sound baffle in an auditorium). Also, acoustic surfaces can be constructed into acoustic enclosures such as music practice rooms, recording studios, and other rooms where fidelity of sound is important.

[00069] Speaker cones of the present invention can replace all types of conventional speaker cones that are used in amplified acoustic devices in all known environments in which the thermoplastic resin is durable.

[00070] An acceptable speaker cone can have a thickness ranging from about 0.25 to about 6.35 mm (0.010 to 0.25 inches), with the thickness corresponding to the desired frequency range, and need not be uniform thickness, but preferably as thin as allowable to obtain desired performance in a given frequency range.

[00071] Sound baffles of the present invention can replace all types of conventional sound baffles that are used in building materials in all known environments in which the thermoplastic resin is durable. An acceptable sound baffle can have a thickness ranging from about 1.27 to about 100 mm (0.05 to 4 inches), and preferably from about 2.5 to about 50 mm.

[00072] Acoustic enclosures of the present invention can replace all types of conventional enclosures that are used in amplified acoustic devices in all known environments in which the thermoplastic resin is durable.

[00073] Speaker cones and sound baffles can be a single layer or multilayer in construction. The acoustic surface of the present invention is intended, principally, to be the only layer, or the outermost layer of a multilayer structure or assembly or laminate, although it is also possible for the acoustic surface to occupy an interior layer position.

[00074] Also, speaker cones and sound baffles need not have their entire surface made of nanocomposites of the present invention. It is within the scope of the invention that nanocomposites described herein occupy only a portion of the acoustic surface, according to the preferences of those skilled in the art of acoustic engineering. [00075] The invention is not limited to these embodiments. The claims follow.

Claims

What is claimed is:

1. An acoustic surface-comprised of a nanocomposite, wherein the nanocomposite comprises a thermoplastic matrix and organoclay at least partially exfoliated therein.

2. An acoustic speaker having a acoustic surface of Claim 1.

3. The acoustic speaker of Claim 2, wherein the acoustic surface is in the shape of a cone.

4. An acoustic baffle having an acoustic surface of Claim 1.

5. An acoustic enclosure having an acoustic surface of Claim 1.

6. The acoustic surface of Claim 1 , wherein the thermoplastic matrix is selected from the group consisting of polyolefins, polyhaloolefins, poly(meth)acrylates, polyamides, polyimides, polyesters, polycarbonates, and combinations thereof.

7. The acoustic surface of Claim 1, further comprising an impact modifier dispersed in the thermoplastic matrix.

8. The acoustic surface of Claim 1 , wherein the nanocomposite is an outer layer in a multilayer structure, acoustic

9. The acoustic surface of Claim 1 , wherein the nanocomposite is a portion of the acoustic surface.

10. The acoustic surface of Claim 1 , further comprising a flame retardant dispersed in the thermoplastic matrix.

11. The acoustic surface of Claim 1 , further comprising in the thermoplastic matrix at least one of fillers, antioxidants, stabilizers, lubricants, pigments, biocides, and combinations thereof.

12. An acoustic surface of Claim 1 wherein the acoustic surface is foamed.

13. An acoustic speaker having an acoustic surface of Claim 11.

14. An acoustic baffle having an acoustic surface of Claim 11.

15. An acoustic enclosure having the acoustic surface of Claim 11.

16. An acoustic surface of Claim 1, wherein the acoustic surface is metallized.

17. An acoustic speaker having an acoustic surface of Claim 16.

18. An acoustic baffle having an acoustic surface of Claim 16.

19. An acoustic enclosure having the acoustic surface of Claim 16.

20. The use of a nanocomposite to make an acoustic surface.