Electronics

5  Electronics 5.1 Introduction

5.2  Electronic Devices

The electronics industry has made considerable efforts to improve its environmental profile, primarily by optimizing the energy efficiency of products and devices, and the sustainability of the materials it uses. Biopolymers can be used in place of oil-derived equivalents in a number of electrical and electronic applications such as wires and cables, housings or casings, and parts of electronic devices. The biopolymers used include biodegradable and nonbiodegradable polymers derived from renewable resources, and biodegradable polymers derived from fossil fuel resources (see also Chapter 1; Section 1.2). The last years have witnessed the miniaturization of electronic devices such as circuit boards, which are difficult to repair and sometimes hard to recycle. Biodegradable polymers can reduce the amount of waste electrical and electronic equipment. In order for a biodegradable polymer to be used in electrical and/or electronic devices, it must possess high mechanical strength and heat resistance. However, the thermomechanical and electrical properties of these polymers remain inadequate for electrical and electronic applications. Recent developments claim the production of biodegradable polymers of high temperature resistance and mechanical strength. Another alternative involves the use of biocomposites for the manufacture of components and accessories of consumer electrical and electronic devices. Biocomposites include materials containing a biopolymer in conjunction with structural reinforcement materials such as carbon, plant, or wood fiber. Engineering thermoplastics made at least in part from renewable resources are used nowadays often in the electronics industry. These bio-based thermoplastics reduce use of fossil fuels without reducing performance. However, stringent product requirements have slowed the adoption of bio-based polymers for the electronics industry.

Among the potential applications in the electronics industry where bio-based alternatives can displace fossil fuel-based polymers, thermoplastic housings and/or enclosures are considered to be the most easily addressed application. Electronic device housings are a particularly demanding materials application. They provide protection of internal components from impact and from contamination. It is thus imperative that the materials used for electronic device housings have high impact resistance. Additionally, electronic devices such as mobile phones often have antenna inside of housing protected by cover. For optimal functioning of a mobile telephone, it is often necessary for the cover be as transparent as possible to electromagnetic radiation having frequencies in the range of about 40  MHz–6  GHz and that the material’s response to such electromagnetic radiation not vary significantly as a result of environment conditions such as temperature and relative humidity. Otherwise, the amplitude of the radio signals sent and received by the telephone can be affected, resulting in a lost or weakened connection or requiring increased power consumption to maintain a signal at a desirable level (2009, WO2009137548 A1, DU PONT). From the bio-based thermoplastics that could replace polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend, which has been the material of choice for electronic housings and enclosures, those based on poly(lactic acid) (PLA) hold the greatest promise. However, PLA is brittle, and more difficult than PC/ABS to render it flame resistant. Therefore, PLA was compounded with various additives and/or blended with other polymers to overcome these handicaps. In this context, enclosure covers for server products were molded from blends of polycarbonate and PLA (20–40 wt%) that compete favorably with flameretardant PC/ABS with respect to physical properties. The renewable resins passed all technical qualifications required for use in IT hardware [1]. NEC developed a

Biopolymers: Applications and Trends. http://dx.doi.org/10.1016/B978-0-323-35399-1.00005-3 © 2015 Published by Elsevier Inc. All rights reserved.

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flame-retardant PLA composite with durability that exceeds flame-retardant fossil fuel-based polymers used in conventional consumer electronic devices such as personal computers (PCs) [2]. JP2005023260 A (2005, TORAY INDUSTRIES) discloses a housing for an electrical/electronic device (e.g., sockets, switches, capacitors, notebooks, mobile phones, recording media, etc.) manufactured by molding a composition comprising 100 pbw of a biodegradable polymer such as PLA, and 1–350 pbw of an organic filler selected from paper flour, wood flour, or kenaf fiber; at least 50 wt% of the paper flour is waste paper flour. KR100899642 B1 (2009, TAE WON SISCHEM CO LTD.) discloses a mobile phone case made of a biodegradable polymer composition comprising: (1) PLA (100 pbw); (2) a reinforcing agent (10–40 pbw) such as talc, glass fiber, and carbon fiber; and (3) a chain extender (1–8 pbw). The PLA consists of crystalline PLA (55–98 wt%) and amorphous PLA (2–45 wt%). The mobile telephone case formed using the biodegradable polymer composition is claimed to have excellent impact strength, tensile strength, and flexural strength. The chain extender contains an isocyanate-type compound selected from hexamethylene diisocyanate, toluene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate or triisocyanate, an epoxy-type compound such as bisphenol A diglycidyl ether, terephthalic acid diglycidyl ether, trimethylolpropane diglycidyl ether or 1,6-hexanediol diglycidyl ether, or an acrylic compound. The biodegradable composition may further contain poly(ε-caprolactone) (PCL) or polyhydroxyalkanoate (PHA) (0.01–30 pbw) with respect to PLA (100 pbw). JP2004175831A (2004, FUJITSU LTD.) discloses a housing for an electronic device made of a biodegradable composition comprising PLA, glass fibers, and a phosphate flame retardant (see Figure 5.1). The lowering of the fluidity caused by the filling of the glass fibers can be suppressed by the addition of the phosphate flame retardant. The housing is claimed to have high strength, excellent moldability, flame retardancy, and biodegradability. The biodegradable housing can be used in electronic devices, such as notebooks, PCs, mobile telephones, and personal digital assistants (PDAs). JP2007231034 A (2007, FUJITSU LTD.) is a modification of the previous patent application, wherein a natural fiber (kenaf fiber) is impregnated with a flame retardant (sodium polyborate). The impregnated material is mixed with a filler, a crystal

Biopolymers: Applications and Trends

Figure 5.1  Model of the housing used as liquid crystal display front cover of a notebook personal computer (2004, JP2004175831 A, FUJITSU LTD.).

nucleating agent, and PLA. The material is kneaded in a proper blending ratio and pelletized to give the material for a housing of an electronic device having high heat resistance and high rigidity. JP2009108328 A (2009, FUJITSU LTD.) is another modification of the last two patent applications, wherein the housing is made of a blend of PLA and polystyrene. Alternately, the housing is made of a blend of PLA and polycarbonate. Example: PLA (Lacea® H-100J, Mitsui Chemicals), polystyrene (Styron, H8652, Asahi Chemicals), glass fiber (CS03JAFT592, Asahi Chemicals), a modifier (copolymer of lactic acid-succinic acidpolypropylene glycol = 50/30/20 wt% or sebacic acid-1,3-butane diol), and a silicone flame retardant (MB50-315, Dow Corning) were kneaded to form a molding material. The obtained material was molded to form a housing claiming to have excellent heat resistance, rigidity, flame retardancy, weather resistance, bending strength, and impact strength. US2006276582 A1 (2006, FUJI PHOTO FILM CO LTD.) discloses a member for electronic device made of PLA (20–80  pbw) and polycarbonate (20–70 pbw). A phosphorus- or a silicon-containing flame retardant (0.5–35 pbw) and a reinforcing fiber (vegetable or glass fiber) (0.1–50 pbw) are also used. The electronic member could be used as electrophotographic copier, printer, or facsimile machine and as for example, copy receiving tray, paper feed tray, and document tray. The electronic member is claimed to be biodegradable, and have excellent flame retardancy and impact resistance. JP2007191547 A (2007) and JP2007191548 A (2007) of TEIJIN CHEMICALS LTD.; TEIJIN LTD. discloses an exterior part of an electronic device (e.g., housing of notebook, scanner, electronic camera, etc.) made of a stereocomplex PLA (scPLA). An scPLA is

5: Electronics

obtained by blending poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) in a one-to-one ratio in the presence of suitable stereocomplex catalysts [3] (see also Chapter 1; Section 1.4.1.1.1). The exterior part is formed by injection molding the scPLA, at a die temperature of 80–130 °C. The electronic component further contains a nucleating agent such as talc (0.01–5 pbw), an inorganic filler (0.3–200 pbw), and a terminal blocking agent (0.01–5 pbw), with respect to PLA component (100 pbw). The scPLA, which has a melting temperature of at least 195 °C, endows the exterior part with enhanced heat resistance. WO2011052252 A1 (2011, PANASONIC ELEC WORKS CO LTD.) discloses a housing for an electronic device made of a PLA-based composition comprising scPLA (50–98 wt%) a complex (1–20 wt%) containing glycidyl methacrylate and silicone/acrylic composite rubber, and talc (1–30). The PLA-based composition is used in mobile phone holders, internal chassis components of mobile telephones, etc. WO2012114397 A1 (2012), WO2013046487 A1 (2013), and US2013035450 A1 (2013) of PANASONIC CORP. disclose a housing for an electronic device such as a flat display device molded from a flame-resistant composition comprising at least 50  wt% PLA and/or lactic acid copolymer, and silica–magnesia catalyst particles as a flame retardant (0.5–9 wt%). An organometallic compound is attached to all or part of the surfaces of the silicamagnesia catalyst particles. Flat display devices include liquid crystal displays, organic EL displays, plasma displays, and the like (see Figure 5.2). The flexural strength of the PLA composition is at least 40 MPa. The housing is biodegradable, does not generate machine noise, and has a glossy surface having a 20° specular glossiness (Gs(20)) of at least 60 (measured according to JIS Z 8741). WO2013031055 A1 (2013, PANASONIC CORP.) discloses the decoration of the previously described housing with a decorative sheet (14) including a decorative layer (15) formed on one surface of the sheet containing a PLA-based composition provided on the base material (13) such that the decorative layer (15) and base material (13) face each other (see Figure 5.3). The coated housing is claimed to have excellent mechanical strength and external appearance, and suppressed generation of defects, for example, weld, color stripe, and partial color difference. US2007172663 A1 (2007, FUJITSU LTD.) discloses an article made of a biodegradable polymer such as PLA to be used as the housing of a mobile

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Figure 5.2 Front elevation view of a liquid crystal display device (2012, WO2012114397 A1; 2013, WO2013046487 A1; 2013, US2013035450 A1, PANASONIC CORP.). 1, Display device body; 2, Stand; 3, Liquid crystal display panel; 5, Outer housing; 6, Front cabinet; 6a, Opening; 6b, Speaker grille.

Figure 5.3 Cross-sectional view of the coated housing of a liquid crystal display device (2013, WO2013031055 A1, PANASONIC CORP.). 13, Base material; 14, Decorative sheet; 15, Decorative layer; 15a, Decorative portion; 16, Adhesive layer.

phone. A base or body made of PLA is coated with a coating film containing a conductive material. The coating film functions as a shield for electromagnetic waves, a ground, and the like. Sandblast may be employed to remove the coating film off the surface of the base after the end of its service life. The base can eventually be decomposed in the ground. JP2011089006 A (2011, FUJITSU LTD.) discloses an electronic device (e.g., notebook or mobile phone), whose housing is coated with a coating composition comprising an emulsion containing PLA, water, and an organic solvent (<10 wt%) having a boiling point above 100 °C. Preferably, two or more kinds of organic solvents different in boiling point are contained, and a content of an organic solvent having the lowest boiling point is lower than that of an organic solvent having the highest boiling point. The organic solvent(s) is selected from the diethylene glycol butyl methyl ether, propylene glycol

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monomethyl ether, ethylene glycol monobutyl ether, and ethylene glycol monomethyl ether. WO2013047285 A1 (2013, NEC CORP.) discloses a case for an electronic device (1) comprising: a base (10) that is mainly formed of PLA; an adhesion layer (20) that is coated over the base and is mainly formed of PLA; a resin layer (30) that exhibits good adhesion to the adhesion layer (20) and can be plated with a metal; and a metal plating (40) that is provided on the resin layer (see Figure 5.4). The adhesion layer comprises preferably PLA, a natural product-based tackifying resin, an antihydrolysis agent, and a polyfunctional isocyanate. The disclosed case is biodegradable having sufficient electromagnetic shielding performance and a metal plating that exhibits good adhesion. JP2009013232 A (2009, KANEKA CORP.) discloses a thermoplastic composition used for exterior cladding of a PC, mobile telephone, and handheld game machine, comprising a PHA copolymer and an inorganic compound. The copolymer is preferably poly(3hydroxybutyrate-co-3-hydroxy hexanoate) containing 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx) repeating unit in a molar ratio of 99/1–80/20. The copolymer has a weight average molecular weight (Mw) of 300,000–3,000,000. The inorganic compound has heat conductivity of preferably 20 W/mK, and is preferably selected from boron nitride, aluminum nitride, silicon nitride, aluminum oxide, magnesium oxide, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, beryllium oxide, and/or diamond. The volume ratio of the copolymer and the inorganic compound is 5/95–95/5. JP2010143978 A (2010, RICOH CO LTD.; AGRI BIOINDUSTRY KK; UNIV HOKKAIDO) discloses a biodegradable composition used as housing of an electrical/electronic device comprising a blend of two PHAs. Each PHA consists of a 3HB and another hydroxyalkanoate such as 3-hydroxyvalerate (3HV). The biodegradable composition includes: a

PHA (A), wherein a percentage content of the 3HB unit is ≥90 mol% and its Mw is 100,000–2,000,000; and a PHA (B), wherein a percentage content of the 3HB unit is ≥70 mol% and <90 mol%, and its Mw is 100,000–2,000,000. A crystallization nucleating agent may be included (e.g., talc or metal salt-type material with a phenyl group or a benzoyl compound type). WO2007088920 A1 (2007) and US2008207844 A1 (2008) of SUMITOMO ELEC FINE POLYMER INC. and SONY CORP. disclose an exterior member for electronic devices, such as an externally connecting terminal cap of a mobile phone, comprising a biodegradable polyester mixed with a polyfunctional monomer, where the biodegradable polyester has a crosslinked structure with a gel fraction (dry weight of gel portion/ initial dry weight) of 50–90%, a flexural modulus of 100–400 MPa, and a Young’s modulus of 60–240 MPa. The biodegradable polyester is preferably selected from poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate-co-adipate) (PBSA), and poly(butylene succinate-co-lactide), alone or as a mixture of two or more thereof in an amount of at least 50 pbw, more preferably 80 pbw, per 100 pbw of the biodegradable polyester composition. The polyfunctional monomer is a monomer capable of being crosslinked by ionizing radiation, such as triallyl isocyanurate, but an acrylic or methacrylic polyfunctional monomer having two or more double bonds within one molecule is suitably used. A cap (3) covering an opening (2) provided in the portion for the connection to an external terminal of a mobile phone (1) is shown in Figure 5.5. The cap (3)

Figure 5.4 Cross-sectional view of an electronic device case (2013, WO2013047285 A1, NEC CORP.). 1, Case of electronic device; 10, Base material; 20, Adhesion layer; 30, Resin layer; 40, Metal plating.

Figure 5.5 Different views of a mobile phone equipped with a cap (2008, US2008207844 A1, SUMITOMO ELEC FINE POLYMER INC.; SONY CORP.). 1, Mobile phone; 2, Opening; 3, Cap.

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is molded from a heat-resistant biodegradable polyester composition and produced by the following procedure: A biodegradable polyester blend is prepared by blending 60–100 pbw PBAT (Ecoflex®, BASF), 0–40 pbw PBSA (Bionolle® 3001, Showa Highpolymer Co. Ltd.), and 6–13 pbw PLA (Lacea® H-280, Mitsui Chemicals, Inc.). A pellet of the obtained biodegradable polyester blend is softened by heating, or degraded in a solvent where the biodegradable polyester blend can be dissolved. Subsequently, the biodegradable polyester is softened by heating, and trimethylolpropane trimethacrylate was added as the polyfunctional monomer in an amount of 5–10 pbw per 100 pbw of the biodegradable polyester. The system is mixed with stirring to equalize the polyfunctional monomer. Thereafter, the solvent may be further removed by drying. The obtained composition is again softened by heating, and molded into a cap (3) shape. The obtained biodegradable polyester-molded article is then irradiated with ionizing radiation to crosslink the biodegradable polyester. Irradiation of electron beams by an electron beam accelerator is preferred, and the irradiation dose is selected from the range of 50–150 kGy according to the blending amount of polyfunctional monomer so that the gel fraction of the heat-resistant biodegradable polyester obtained after irradiation becomes 50% or more. WO2005054359 A1 (2005, SONY CORP.) discloses an electronic product including, as a constituent element thereof, a molded product manufactured by molding a biodegradable composition comprising: at least one polysaccharide, a flame-retardant additive containing a metal hydroxide, and a hydrolysis suppressing agent for suppressing the hydrolysis of the polysaccharide. The polysaccharide is cellulose, starch, chitin, chitosan, dextran, one of derivatives thereof, or a copolymer containing at least one thereof. The metal hydroxide is at least one of aluminum hydroxide, magnesium hydroxide, and calcium hydroxide. The flame-retardant additive may further contain a nitrogen oxide compound. The hydrolysis suppressing agent is a carbodiimide compound, an isocyanate compound, or an oxazoline compound. The molded product may be used as housing for several electronic products including: stationary AV equipment, such as a DVD (digital versatile disc) player, CD (compact disc)

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player, MD (mini-disc) player, or an amplifier, loudspeakers, car-laden AV/IT equipment, PDA inclusive of electronic books, video decks, projectors, TV receivers, monitors, digital video cameras, digital still cameras, printers, radio receivers, radio receiver/tape recorder, a system stereo, microphone, headphone, keyboards, headphone stereo, portable CD players, portable MD players, portable audio devices, such as so-called silicon audio players, refrigerators, laundry machines, air conditioners, PCs, peripherals of the PCs, stationary TV game machines, mobile phones, telephone sets, facsimile machines, copying machines, and entertainment robots. WO2008050945 A1 (2008) and KR100836271 B1 (2008) of KOREA ENERGY RESEARCH INST disclose a method for manufacturing an electronic parts case using biocomposites reinforced with seaweed fiber. The method, as outlined in Figure 5.6, comprises the steps of: (S100) drying seaweed fibers; (S101) shattering the dried seaweed fibers; (S102) drying, shattering, and dissociating the seaweed fibers into fine fibers; (S200) dehydrating a polymer reagent by drying; (S201) grinding a polymeric reagent selected from a biodegradable polymer and a general polymer into a powdery form; (S300) mixing the seaweed fiber particles with the polymeric reagent powder to prepare an integral mixture of the seaweed fiber and the polymeric reagent powder; (S400) filling a metal mold with the mixture; and (S500) compression molding the metal mold under elevated pressure at a high temperature to prepare a biocomposite. In step (S102), the fine seaweed fiber particles are obtained by grinding dissociating the seaweed fiber at 5000–10,000 rpm for 25–100 s with a high-temperature grinder. According to one embodiment of the present invention, one of biodegradable polymers, namely poly(butylene succinate) (PBS) is used as the polymeric reagent. Of seaweeds, read algae are preferred because of their low thermal expansion rate. Red algae fibers exhibit substantially equivalent crystallinity and superior thermal stability, as compared to cellulose. When the red algae fibers are used in heat-generating cases for electronic parts, they minimize thermal strain caused by temperature increase, thus stably supporting and protecting the electronic parts. Most of the commented biodegradable polymers have inferior mechanical properties. Bio-based thermoplastic

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Figure 5.6 Flow chart illustrating a method for preparing a seaweed fiber-reinforced biocomposite (2008, WO2008050945 A1, KOREA ENERGY RESEARCH INST).

polyamides (PAs) are a viable alternative material for use in making housings of electronic devices. Thermoplastics exhibit good physical properties and are conveniently and flexibly molded into a variety of articles of varying degrees of complexity and intricacy. WO2009137548 A1 (2009, DU PONT) discloses an electronic device housing made of a renewable thermoplastic composition comprising: (1) 70.1– 100 wt% of at least one PA derived from renewable resources selected from PA 910; PA 912; PA 914; PA 916; PA 936; PA 610; PA 612; PA 614; PA 616; PA 618; PA 636; PA 1010; PA 1012; PA 1013; PA 1014; PA 1015, PA1016; PA 1018; PA 1036; PA 10T/1010; PA 101/1010; PA 1210; copolymers of two or more thereof; and blends thereof; at least one PA having a carbon content of at least 50% (measured in accordance with the ASTM-D6866 Bio-based Determination Method); (2) 0–29.9 wt% of at least one fibrous reinforcing agent having circular type cross-section; (3) 0–14.9 wt% of at least one fibrous reinforcing agent having noncircular-type cross-section; (4) 0–29.9 wt% glass flake; (5) 0–29.9 wt% of at least one mineral reinforcing agent; and (6) 0–29.9 wt% of at least one impact modifier agent. Thermoplastic PAs derived from renewable resources are used nowadays often in the electronics

industry. Suitable materials include PAs such as PA 1010 and PA 610. One commercial product of such PAs is Zytel® RS HTN (Du Pont), which is a partly renewably sourced specialty PA compound made with bio-based sebacic acid. Zytel® RS HTN properties include impact resistance, stiffness, and low warpage. Zytel® RS HTN is recommended for electronic applications requiring radio wave transparency, such as handheld devices, mobile phones, GPS, PDAs, radios, and cameras.

5.2.1  Commercial Products Hereafter is an overview of commercial biopolymer-based housings and enclosures of electronic devices: • Bioserie iPhone 5 cover made of PLA (Ingeo®, NatureWorks) [4]. •  Biodegradable iNature iPhone case cover, of Med Computer made of a biodegradable polyester urethane elastomer (Apinat®, A.P.I- Biomood Srl). • Telecom Italia’s Eco cordless telephone made of PLA (Ingeo®, NatureWorks) [5].

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•  Ventev™ Element iPhone 3G case made of 100% Naturacell™ (Rotuba Extruders Ltd.), a blend a natural-based plastic softener with Eastman™ cellulosics derived from the pulp of softwood trees [6]. •  Fujitsu’s computer keyboard is made of cellulose acetate (Biograde® C 7500, FKuR); the palm rest is made of lignin (Arboform®, Tecnaro GmbH) and injection molded by Amper-Plastik GmbH [7]. • Fujitsu’s optical USB mouse (M440) made of cellulose acetate (Biograde® 7500, FKuR) [8]. •  Outer casing of Samsung’s mobile phone Samsung Reclaim™ made of a blend of PLA (40  wt%) and polycarbonate (60  wt%). This material is mostly used on the rear side and battery cover of the device [9]. •  Housing of Kuender touchscreen PC (21.5″) made of bio-based scPLA (Supla™ 155, Supla (SuQian) New Material Co., Ltd.); scPLA is based on lactides from Corbion Purac [10]. • Printers and multifunction printers of Oki Data Corp. contain bio-based parts consisting of at least 25 wt% PLA [11]. • Drum cover of Fuji Xerox Copy Machine made of a blend of polycarbonate and cellulose (c. 40 wt%) [12]. • Terminal cover on the back of Sony ultraslim OLED TV made of bio-based PA 11 [13]. • Body cap of Sony Digital SLR 350 camera made of bio-based PA [14]. • Mobile healthcare (mHealth) electronic devices made of bio-based high-performance PAs (Kalix® HPPA 200 series (based on PA 610) and 3000 series, Solvay Specialty Polymers) [15]. • Tanita bathroom scale made of a PLA blend (Terramac®, Unitika Ltd.) [16]. • Bio-based solar panel backsheet for Si-based photovoltaic solar cells made of BioBacksheet™ (BioSolar Inc.), a two component system that is highly water resistant and contains high dielectric strength material combined with cellulosic film [17]. • Bionic fans of Ziehl-Abegg made of bio-based PA 610 (Akromid S, Akro-Plastic). Bionic fans (not in market yet) to be used in refrigeration technology (cold chain to the supermarket),

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heaters and heat pumps, and for electronics cooling (computing centers and switchgear-cabinet and inverter cooling) [18].

5.3  Audio Devices A material characteristic required for a speaker diaphragm is the sound velocity (C) (m/s). The sound velocity, C, can be calculated from the equation: C = (E/ρ)0.5, where E is the Young’s modulus and ρ is the density of the material. When a material is hard and lightweight (or has large rigidity and low density) as being ideal conditions for the diaphragm material, a value of the sound velocity is large, and that is more ideal. There is generally a correlation between the sound velocity and a high limit frequency of the speaker, in which the speaker is required to reproduce sound up to about 20 kHz as an audible frequency threshold for humans, and for satisfying this requirement, the sound velocity is required to be C > 1800 m/s (2010, WO2010004717 A1, PANASONIC CORP.). One of the biopolymers considered as a replacement of conventional polymers for the manufacture of speaker diaphragms is PLA. Generally, PLA has a high specific gravity and practically has difficulty in obtaining a sufficient sound velocity C > 1800 m/s, and hence PLA has not been used for a speaker diaphragm. A stretched PLA film is known to exhibit piezoelectricity (piezoelectric modulus of about 10 pC/N at normal temperature) (1993, JPH05152638 A, TAKIRON CO). However, the piezoelectric effect obtained by mere stretching of PLA is not considered adequate for practical applications. JP2005213376 A (2005, MITSUI CHEMICALS INC.) discloses a PLA film of enhanced piezoelectricity obtained by stretching a PLA-based piezoelectric material containing PLA and inorganic nanoparticles. The inorganic particles are made of compounds of group II element compounds, preferably calcium compounds, metal oxides, preferably silicon oxide or titanium oxide, and/or layered inorganic compounds, preferably clay minerals. The compounded PLA has high piezoelectricity, transparency, and workability, and it can be used for a speaker, a microphone, headphones, etc. GB2412269 A (2005, SONY CORP.) discloses an acoustic paper diaphragm used in speakers formed from paper in which a PLA emulsion is added as a biodegradable sizing agent. This provides an acoustic

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paper diaphragm that is both moisture resistant and biodegradable. JP2005260546 A (2005, KENWOOD CORP.) discloses a speaker diaphragm (10) for the sound wave generating unit of a speaker used by an audio device, comprising PLA and kenaf fiber (5–20 wt%) (see Figure 5.7). The speaker diaphragm is biodegradable, and is claimed to have high glossiness and excellent design. JP2007312286 A (2007, KENWOOD CORP.) is a modification of the previous patent application, wherein the speaker diaphragm comprises a mixture of PLA (45–55 wt%), polypropylene (20–30 wt%), and cellulose fibers (e.g., pulp) (20–30 wt%). When kenaf fibers are mixed into PLA, the diaphragm becomes apt to break when the amount (wt%) of the kenaf fibers exceeds a certain percentage of a total weight. Moreover, in the case of further mixing a binder for the purpose of increasing compatibility of the mixed material to improve the sound velocity, an appropriate kind and a weight ratio of the binder vary depending upon a kind and mixed ratios of the material into which the binder is mixed. Therefore, mixing the binder may just lower the sound velocity, and it has been difficult to select an appropriate binder in accordance with a material into which the binder is mixed (2010, WO2010004717 A1, PANASONIC CORP.). JP2008193477 A (2008, MATSUSHITA ELECTRIC IND CO LTD.) discloses a speaker box made of a mixture of PLA and bamboo fibers (10–70 wt%). The speaker box is biodegradable and claimed to 12 29 10

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have improved high quality, reliability, sound quality, heat resistance, and strength. JP2009246704 A (2009, PANASONIC CORP.) discloses a frame for a speaker formed by injection molding a composition comprising PLA, a bamboo fiber, and optionally a synthetic polymer (e.g., polypropylene, polycarbonate, and styrene-butadiene rubber). The bamboo fiber contains bamboo powder and carbonized bamboo powder. The content of the bamboo fiber is 5–70 wt%. The frame is light in weight, and maintains sufficient rigidity, thus reducing resonance of the frame and providing flat sound pressure frequency characteristic of the speaker, and hence reducing distortion. WO2009011102 A1 (2010, PANASONIC CORP.) is an alternative of the previous patent application disclosing in one of its embodiments a speaker diaphragm comprising PLA, carbonized bamboo powder, and further bamboo powder or microfibrillated bamboo fiber (5–55 wt%). WO2010004717 A1 (2010, PANASONIC CORP. is also a modification of the previous patent applications, wherein a speaker diaphragm (1) comprises PLA (1A), a bamboo fiber (1B), and a natural binder (1C) (see Figure 5.8). A microfibrillated bamboo fiber is preferably used. The natural binder is preferably a starch-type binder: The content of bamboo fiber is 10–30 wt%, and the content of starch-type binder is 1–10 wt%. The speaker diaphragm has specific gravity of 1.10–1.18, and a sound velocity C > 1800 m/s. WO2014010138 A1 (2014, PANASONIC CORP.) discloses an audio device in which the exterior is made of a biodegradable composition comprising at least 50 wt% PLA and/or lactic acid copolymer, at least an inorganic filler (e.g., glass fiber, glass bead, or talc), and a hydrolysis inhibitor (e.g., polycarbodiimide). The resin composition has a loss coefficient of at least 0.04. The molding has a glossy surface having a 20° specular gloss (Gs(20)) of at least 60

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Figure 5.7  Cross-sectional view of a speaker comprising the speaker diaphragm (2005, JP2005260546 A, KENWOOD CORP.). 10, Loudspeaker diaphragm; 12, Speaker; 14, Magnetic circuit; 16, Voice coil; 18, Damper; 20, Flame; 22, First plate; 24, Magnet; 26, Second plate; 28, Center pole; 29, Front panel.

Figure 5.8  Cross-sectional view of a speaker comprising a speaker diaphragm (2010, WO2010004717 A1, PANASONIC CORP.). 1, Speaker diaphragm; 1A, PLA; 1B, Bamboo fiber; 1C, Natural binder.

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(measured in accordance with JIS Z 8741). The audio device is claimed to have an excellent resonance peak characteristic in the low range and excellent quality. The audio equipment is used for speaker apparatus, stereo component, CD player, mini-component, car audio player, portable music player, integrated circuit recorder, audio equipment of display apparatus, for example, liquid crystal display, organic electroluminescent display and plasma display, and plane-type built-in speaker (see Figure 5.9). WO2004052047 A1 (2004, SONY CORPORATION) discloses an audio apparatus housing made of a composite material comprising a biodegradable polymer, an inorganic material, and a hydrolysis inhibitor. The biodegradable polymer is selected from polysaccharides, aliphatic polyesters, poly(amino acid)s, poly(vinyl alcohol), polyalkylene glycol, and/or their copolymers. The aliphatic polyester is selected from PLA, poly(3-hydroxybutyrate)

Figure 5.9 Perspective view explaining the external appearance of the speaker apparatus (2014, WO2014010138 A1, PANASONIC CORP.). 1, Speaker apparatus; 2, Front cabinet; 3, Back cabinet; 4, Speaker network; 5, Stand.

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(P3HB), poly(3-hydroxyvalerate), PCL poly(ethylene succinate), PBS, poly(butylene adipate), poly(malic acid), and/or their copolymers. A preferred biodegradable polymer is PLA (Lacea® H100J, Mitsui Chemicals). Examples of inorganic materials include inorganic hydroxide compounds, such as aluminum hydroxide, magnesium hydroxide, or calcium hydroxide; an inorganic salt, such as barium sulfonate or calcium carbonate; an inorganic oxide compound, such as titanium oxide or alumina; and an inorganic silica compound, such as mica or talc. The hydrolysis inhibitor is added for preventing the acoustic apparatus housing from easily decomposing due to, for example, moisture in air during the period of use of the acoustic apparatus. A preferred hydrolysis inhibitor is a carbodiimide compound since it can be melt-kneaded with the biodegradable polymer compound and the carbodiimide compound added in a small amount can inhibit hydrolysis. The material for audio apparatus housing is claimed to be excellent in output acoustic pressure level and distortion ratio as well as flatness compared to a conventional material for acoustic apparatus housing. From the viewpoint of obtaining excellent tone quality, it is preferred that the material for acoustic apparatus housing has a higher specific gravity, preferably a specific gravity of about 1.3 g/cm3 or more, more preferably about 1.35 g/cc or more, most preferably about 1.40 g/cm3 or more. Niägele and Eisenreich, both of Tecnaro GmbH (2011) developed two types of loudspeaker housings made of a mixture consisting of lignin (40–70 wt%), vegetable fibers (30–60 wt%), and natural additives (<10 wt%). The various components were mixed using a standard mixer and pelletized at ambient temperature to form granules. The granules were processed at relatively low temperatures by standard injection molding machines (140–170 °C) to manufacture the housing parts of complex loudspeaker designs. Two types of loudspeaker housings were designed and manufactured according to the procedures described above. Depending on the fiber content, the Young’s modulus can vary between 2 and 8 GPa and the Charpy impact strength between 2 and 6 kJ/m2. The elongation at break is between 0.3 and 0.6%. The thermal expansion coefficient establishes below 5 × 10−5 1/K. Nearly, no resonance frequencies are found and a strong damping of vibration leads to excellent acoustic properties, which enables the material to be used in loudspeaker applications [19].

242

5.3.1  Commercial Products Here are a few commercial audio devices using biopolymers: •  Loudspeaker casing made from PLA blend (Corbion EuBP/Zabel) [20]. •  Noisezero O+ Eco edition over-headphones have been constructed using cornstarch (EOps). It uses cornstarch biopolymer for the earbuds and the microphone housing [21].

5.4  Printed Circuit Boards Traditionally, printed circuit boards (PCBs) are mainly manufactured from layers of thin sheets of thermoset resins, such as epoxy resin (with the exception of inorganic materials such as ceramics), which are applied on to a woven fabric or a random dispersion of high modulus organic (carbon or aramid) or inorganic (glass) fibers. The impregnated fabrics are laminated together and cured to achieve the final shape and desired electrical and mechanical characteristics. These laminates can be drilled, metalized, and patterned to create vias and interconnection wiring. Electronic components are then attached to the laminates by lead-containing solders. The amount of PCBs manufactured in this way is substantial. It has been estimated that the worldwide production of PCBs in 2005 required 52 × 106 m2 of laminate and 270 × 106 m2 of impregnated fabric [22]. In the electronics industry, about 1.5 × 106 tons of epoxy resins derived from fossil fuel resources are processed annually for circuit boards, PCBs, and similar [23]. Thermoset resins are not meltable, and it is difficult to separate and recover wiring metals. Furthermore, the thermosetting resin of a PCB does not decompose and remains semipermanently at the site, where it is disposed of and buried. The incineration of discarded PCBs is expensive and generates toxic wastes (1997, WO9711109 A1, IBM). Most current PCBs contain brominated flame retardants, which are classified as neurotoxic and carcinogenic [24]. On the other hand, thermosetting resins derived from renewable resources have historically lacked the strength and environmental resistance of thermoset resins like epoxy resins derived from fossil fuel resources [24]. Lincoln et al. (2008) [24] proposed a biocomposite for PCB that is based on epoxidized linseed oil,

Biopolymers: Applications and Trends

melamine polyphosphate for flame retardancy, and woven flax fiber for reinforcement. The melamine polyphosphate in thermoset systems is an effective flame retardant of low environmental impact in terms of toxicity and resource consumption. To improve moisture resistance, the flax fibers were treated with sodium hydroxide and octadecyltrichlorosilane. A PCB prototype made from these materials is claimed to be a viable alternative to current PCBs; it has potentially lower environmental impact, is cheaper, and it has satisfactory thermal, electrical, and mechanical properties. WO9711109 A1 (1997) and US5833883 A (1998) of IBM disclose a bio-based PCB comprising a plurality of sheets of fiberglass or bio-based cloth impregnated with a crosslinked polymer consisting of lignin, crop oils, wood resins, tannins and/or polysaccharide resins, and optionally an electrical conductor. The materials used are biodegradable reducing requirement for incineration and derived from renewable resources. Mechanical performance is claimed to be comparable to that of prior art. PCBs fabricated from the lignin-based resin passed most of the standard physical, electrical, and reliability tests for an “FR4”-grade laminate [25]. Although there was an advanced product development, market transfer was not accomplished [26]. There are also proposals for the manufacture of PCBs from biodegradable polymers derived from renewable resources. One of the early efforts was GB2281709 A (1995, FUJITSU LTD.), which disclosed in one of its embodiments an electric circuit substrate made of a composition comprising a biodegradable polymer and an antibiotic to retard biodegradation of the polymer. The biodegradable polymer was selected from PHAs (e.g., P3HB or poly(3-hydroxybutyrate-co-3-hydroxyvalerate)), PCL, denatured starch, and chitin–chitosan. Examples of the antibiotics are 2-(4-thiazolyl)-benzimidazole, 2-(methoxycarbonylamino)-benzimidazole, bis(2-pyridylthio-1-oxide) zinc, diiodomethyl-p-tolyl-sulfone, zeolite/silver, hydroxyapatite/silver, and silica/silver. The antibiotic is added to only the outermost layer of laminate structure of PCB so as to prevent the polymer from being biodegraded. DE19720661 A1 (1998, SCHURIG JUERGEN) discloses a substrate for circuit board having: a layer of biodegradable carrier material (1) comprising a fiber-forming structure; a biodegradable stabilizing material (2) to stabilize the carrier material (1); and a conducting layer (3) (see Figure 5.10). Preferably,

5: Electronics

243

Figure 5.10 Substrate of a circuit board (1998, DE19720661 A1, SCHURIG JUERGEN). 1, Biodegradable carrier material; 2, Biodegradable stabilizing material; 3, Conducting layer.

the biodegradable fiber structure is made of flax, and the biodegradable stabilizing material is starch. Nägele et al. (2005) [27] proposed Arboform® (Tecnaro GmbH) as a matrix for the production of PCBs. Arboform® is a bio-based thermoplastic composed of three natural components: lignin, various cellulose fibers such as hemp and flax, and some natural additives (see Chapter 1; Section 1.12). The authors claim that renewable materials application for PCB is viable, but considerable optimization would be required to achieve satisfactory performance to ensure their acceptance by the electronic industry. Moisture absorption was not specifically examined, but would likely have been a problematic property considering the nature of the reinforcement. A successful implementation of their materials would impart minimal financial burden on the PCB production industry. WO2013144420 A1 (2013, UPM KYMMENE CORP.) discloses a biodegradable substrate (110) for a multilayer PCB (100) made of a mixture of PLA and lignin (see Figure 5.11). The lignin used for the circuit board material may comprise lignin(s) of one or more types (Kraft lignin, sulfite lignin, and soda lignin) and/or lignin from various sources (wood, corn, rice, cotton, and other biological feedstock). The substrate of an embodiment comprises PLA and Kraft lignin extracted from wood. The PLA is selected from PLLA, block copolymer of PLLA and PDLA, and scPLA (see Chapter 1; Section 1.4.1.1.1). A preferred commercial PLA is Ingeo™ 3251 D (NatureWorks). This biopolymer comprises PLLA and a small amount of PDLA (about 1.5%), whereby the melting temperature (Tm) of this biopolymer is relatively low, and its melt flow index (MFI) is high. As the PLA has a high MFI, lignin is easily mixed with the used PLA. The mixing of lignin to PLA may be performed in a temperature above the Tm of PLA. However, when the temperature exceeds 200 °C, the lignin starts to degrade. Therefore, the temperature should be below 200 °C, preferably in the temperature

Figure 5.11  Circuit board comprising a first at least partly electrically conductive layer on a first surface of the circuit board and a second at least partly electrically conductive layer on a second surface of the circuit board (2013, WO2013144420 A1, UPM KYMMENE CORP.). 100, Circuit board; 110, Substrate (PLA and lignin); 120, First electrically conductive layer; 130, Second electrically conductive layer; Ts, Thickness of the substrate.

range from 170 to 200 °C, most preferably at 185 °C. This particular temperature was found to give very good viscosity for the PLA–lignin mixture for lignin contents of less than 40 vol%. Alternatively, a highheat PLA such as block copolymers of PLLA/PDLA and scPLA may be used.

5.5 Insulators Conventional insulated wires and cables for electrical/electronic devices include insulators (insulation coatings) made from nonbiodegradable polymers derived from fossil-based resources, such as polyolefins. There have been several attempts to use biodegradable polymers in the field of electric wires and cables. PLA is one of the most studied biodegradable polymers. PLA has excellent electrical insulation properties at temperatures ranging from room temperature to around 70 °C. At temperatures higher than 70 °C, however, the insulation performance of PLA deteriorates due to its poor heat resistance [28]. Furthermore, the basic electrical insulation characteristics of PLA such as volume resistivity, dielectric constant, and dielectric loss tangent measured at room temperature, were found to be almost the same as those of crosslinked polyethylene currently used as insulating material for cables and electric wires. The mean impulse breakdown strength of PLA was about 1.3 times that of crosslinked polyethylene [29].

244

Biopolymers: Applications and Trends

JP2002358829 A (2002, MITSUI CHEMICALS INC.) discloses an electric insulation material for high-voltage electric cable, transmission line, containing PLA. The electric insulation material is claimed to have high dielectric breakdown voltage (it can withstand a high voltage of 1 kV/mm or more) and be biodegradable. PLA has a melting temperature (Tm) of 170 °C that is higher than that of polyethylene, which is typically used as insulation material. For the purpose of imparting heat resistance, it has been considered to crosslink PLA. JP2003051215 A (2003, DAICEL CHEM) discloses a wire coated with an aliphatic polyester, such as crosslinked PCL or a mixture of PCL and PBS. The biodegradable coating is crosslinked by radiation. The core line is preferably an optical fiber. The coated wire is claimed to have increased mechanical strength, heat resistivity at high temperature, and biodegradability. JP2007213900 A (2007) and JP2012069523 A (2012) of FUJIKURA LTD. disclose an insulated wire having an outer layer (12b) containing crosslinked PLA and inner layer (12a) containing ethylene-type polymer, which are laminated on coating portion. The coating portion covers a part of a conductor (11) (see Figure 5.12). The ethylene-type polymer is selected from an ethylene-vinyl acetate copolymer, or an ethylene-acrylate copolymer or an ionomer resin. The crosslinked PLA layer is claimed to provide an insulation wire with excellent heat resistance.

JP2008195873 A (2008, FURUKAWA ELECTRIC CO LTD.) discloses a resin composition for molded product used for insulated wire for optical fiber cord, containing PBS (85–15 wt%) and a block copolymer of poly(alkyl methacrylate) and poly(alkyl acrylate). The resin composition is claimed to provide a molded product having excellent moldability, mechanical characteristics, heat-and-moisture resistance, external appearance, and workability. JP2007042521 A (2007, YAZAKI CORP.) discloses an electric cable (10) having an inclusion (4) formed by mixing filler of wood derivatives with base material and a holding roll tape (5) formed by mixing filler of wood derivatives and biodegradable polymers with base material, in preset weight proportion (see Figure 5.13). In the cable (10), two insulated wire cores (3) are coated with an insulator (2) comprising polyolefin on a conductor (1); the inclusion (4) is interposed to be formed, thereon the holding roll tape (5) is wound up, and covered with a sheath (6) covered with a polyolefin. The base material is selected from polyethylene and poly(ethylene terephthalate) (PET) and regenerated PET. The biodegradable polymer used for the holding roll tape is selected from PLA, PCL, and aliphatic–aromatic copolyesters. The wood derivatives are cellulose, lignin, or hemicellulose. JP2010027387 A (2010, YAZAKI CORP.) is a modification of the previous patent application, in which the inclusion has a circular profile core line

10 12 t1

11

t2 11a 13 DO

DI 13b 13a

12a

12b

Figure 5.12  Insulated wire (2007, JP2007213900 A, FUJIKURA LTD.). 10, Insulation wire; 11, Conductor; 11a, Copper strands; 12, Coating portion; 12a, Inner layer (second layer); 12b, Outer layer (first layer); 13, 13a, 13b, Seams.

Figure 5.13 Insulated wires and cables (2007, JP2007042521 A, YAZAKI CORP.). 1, Wire core (conductor); 2, Insulator; 3, Insulated wire core; 4, Inclusion; 5, Holding roll tape; 6, Sheath; 10, Cable.

5: Electronics

(7) made of paper material, that is coated with a biodegradable polymer (see Figure 5.14). The biodegradable polymer is selected from PLA, PCL, and aliphatic–aromatic copolyesters. In order for a biodegradable polymer to be used as a wire insulator for automobile use, it is required to have not only enhanced mechanical properties but also water resistance, considering the peculiarities of sites where the electric wires are used. However, the bulk of biodegradable polymers made of polyesters do not have sufficient water resistance because of their molecular structures (ester bonds). JP2010238657 A (2010, AUTONETWORKS TECHNOLOGIES LTD.; SUMITOMO WIRING SYSTEMS; SUMITOMO ELECTRIC INDUSTRIES) discloses an insulated wire equipped with an insulator composed of a blend comprising a biodegradable polymer (100 pbw) and a polyolefin (10–50 pbw). Suitable biodegradable polymers include aliphatic polyesters (e.g., PLA, PBS), aliphatic polyester derivatives, polysaccharides (e.g., cellulose), or polysaccharide derivatives (e.g., cellulose acetates). Preferred biodegradable polymers are PLA (V351X51 and V554R10, Toray Industries, Inc.; TCA8070MN, Unitika Ltd.), cellulose acetate (5300-26 and 15300-31, Daicel Corp.), and PBS (NF01U, Novamont -ex Chemitex, Inc.; Bionolle® 1020, Showa Highpolymer Co., Ltd.). The polyolefin is preferably functionalized. A suitable polyolefin is polypropylene. The insulated wire is claimed to have excellent cold resistance and abrasion resistance. The insulated wire is suitable for use in motor vehicles and electric–electronic devices. WO2012063619 A (2012, AUTONETWORKS TECHNOLOGIES LTD.; SUMITOMO WIRING SYSTEMS; SUMITOMO ELECTRIC INDUSTRIES)

245

discloses an insulated wire for electric/electronic devices and motor vehicles comprising a conductor and an insulator made of a PHA having a repeating unit structure represented by the chemical formula of Scheme 5.1. Examples of the monomer units include: 3HB, 3HV, 3HHx, and 3-hydroxyheptanoate. If at least one of R1 and R2 is an alkyl group having two or more carbon atoms, the side chains increase to further improve the water resistance. In addition, the PHA has a sufficient biodegradability even when improved in water resistance. If a  =  b  =  1, the PHA has repeating units of 3-hydroxyalkanoate, which have the advantage of easy availability. In this case, when R1 is an alkyl group having one carbon atom in the general ­formula, the PHA has repeating units of 3HB, which have an excellent biodegradability. In addition, if R2 is an alkyl group having two or three carbon atoms, the PHA contains a copolymer of 3-hydroxyalkanoate containing 3HB. The PHA may contain a dehydrating agent to prevent the hydrolytic degradation of the PHA if the insulator is brought in contact with the water. Examples of the dehydrating agent include carbodiimide, benzotriazole, succinimide, and derivatives thereof. JP2008138060 A (2008, MEIDENSHA ELECTRIC MFG CO LTD.) discloses a powdery insulating composition consisting of PBS. The powdery insulating composition is used mainly for coating a conductor, but also for electric power system such as switchgear and circuit breaker, and high-voltage apparatus. The coating of the conductor is performed by a fluid-soaking method. The conductor is covered after being heated in advance.

Figure 5.14  Insulated wires and cables (2010, JP2010027387 A (2010, YAZAKI CORP.)). 5, Inclusion; 7, Circular profile core line (paper); 8, Biodegradable polymer layer.

246

Biopolymers: Applications and Trends

materials. Hytrel® contains 20–60% of renewably sourced materials.

Scheme 5.1 (2012, WO2012063619 A, AUTONETWORKS TECHNOLOGIES LTD.; SUMITOMO WIRING SYSTEMS; SUMITOMO ELECTRIC INDUSTRIES). R1, R2, Alkyl group having one or more carbon atom: a, b ≥ 1.

5.5.1  Commercial Products • Wire and cable insulators made of bio-based PA (Zytel®, Du Pont) and bio-based thermoplastic polyester elastomer (Hytrel® RS, Du Pont). Zytel® contains at least 38% renewable sourced

• High-performance cable insulator made of biobased PA 1010 (Vestamid® Terra DS, Evonik Industries). • Automotive wire and cable insulators made of Arnitel® Eco (DSM). These materials meet the severe ISO 6277 class D requirements for automotive wire and cable. Arnitel® Eco is a thermoplastic copolyester with 20–50% of its content derived from rapeseed oil [30]. •  Acoustic polyurethane foams derived in part from bio-based polyol (<20  wt%). Although these foams have not yet commercialized, they have been qualified by IBM for use in server computers [1].

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Family members

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Inventors

Applicants

Title

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NAGASHIMA TAKASHI; NAKAO SUGURU; TADA NAOTO

PANASONIC CORP.

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IBM

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