FIELD OF THE INVENTION

The present invention relates to a thin-walled enclosure for an electronic component comprising ignition resistant carbonate composition which achieves a rating of HB, V-2, V- 1 , V-0, 5VA, or 5VB by the UL 94 end product flammability test procedure and methods to make said thin-walled encased electronic component.

BACKGROUND OF THE INVENTION Conventionally, enclosures for electronic equipment comprise injection molded thermoplastic parts such as polycarbonate (PC), acrylonitrile butadiene styrene (ABS), or combinations thereof (PC/ABS). Such enclosures typically need to meet flammability requirements set by agencies such as Underwriters' Laboratories' (UL). Because of injection molding limitations, these parts are usually a minimum thicknesses of from 1.6 to 2.0 millimeters. Because of the trend towards miniaturization or down-sizing of electronic equipment, and more importantly their internal components, wall thickness of less than 1.2 millimeters are essential.

Easy flow carbonate polymer compositions for injection molding are known, for example see USP 6,043,310; 6,939,905; or 7,232,854. However, easy flow comes at a cost, usually by reducing the molecular weight of the carbonate polymer. Lower molecular weight often results in a decrease of one or more critical properties such as impact resistance, environmental stress crack resistance (ESCR), and/or ignition resistance.

Moreover, low molecular weigh compositions often suffer from one or more unacceptable aesthetic problems such as apparent weld lines, silver streaking, jet marks, or burn marks.

It would be desirable to provide thin-walled enclosures for electronic equipment and/or electronic components which maintain a good blend of mechanical properties, specifically impact resistance and aesthetic properties yet fully meet required agency flammability ratings. SUMMARY OF THE INVENTION

The present invention is such an ignition resistant enclosure for an electronic component comprising a pair of shell elements thermoformed from a sheet comprising a carbonate polymer composition and having a thickness of from between 0.5 to 1.2 millimeters adapted to encase said electronic component wherein the shell encased electronic component achieves a rating of HB, V-2, V-l, V-0, 5VA, or 5VB by the

Underwriter's Laboratories' 94 (UL 94) end product flammability test procedure.

In one embodiment of the ignition resistant enclosure described herein above, the pair of shell elements comprises a first shell element and a second shell element wherein the first shell element is dimensionally the same as the second shell element or the first shell element is dimensionally different than the second shell element.

In another embodiment, the ignition resistant enclosure described herein above further comprises one or more insert or structural component within the shell when said shell has encased the electronic component.

In a preferred embodiment, the carbonate polymer composition of the ignition resistant enclosure described herein above comprises one or flame retardant compound selected from a silicon-containing graft copolymer, a monomeric aromatic phosphorous compound, an oligomeric aromatic phosphorous compound, a brominated organic compound, a chlorinated organic compound, a polytetrafluoroethylene polymer, a fluorothermoplast, a metal salt, or a filler.

In another embodiment, the carbonate polymer composition of the ignition resistant enclosure described herein above further comprises a core shell impact modifier, an acrylonitrile, butadiene, and styrene (ABS) terpolymer, a polyester (PES), or mixtures thereof.

In one embodiment, the electronic component of the ignition resistant enclosure described herein above herein is a battery.

Another embodiment of the present invention is a method to provide an ignition resistant enclosure for an electronic component comprising the steps of (i) thermoforming a pair of shell elements from a sheet comprising a carbonate polymer composition and having a thickness of from between 0.5 to 1.2 millimeters adapted to encase said electronic component, (ii) enclosing said electronic component, and (iii) mating the shell elements together with the electronic component encased, wherein the mated shell encased electronic component achieves a rating of HB, V-2, V-l , V-0, 5VA, or 5VB by the Underwriter's Laboratories' 94 (UL 94) end product flammability test procedure.

BRIEF DESCRIPTIION OF THE DRAWINGS

FIG. 1 is an illustration of a shell element of an enclosure for encasing a battery pack.

FIG. 2 is an illustration of a structural component insert providing for four chambers for a batter pack enclosure.

FIG. 3A is an illustration of a shell/insert construction.

FIG. 3B is a magnification of FIG. 3A showing a threaded nut in boss hole.

FIG. 4 is an illustration of a battery pack enclosure comprising two shell/insert constructions mated together. DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a thermoformed front shell element 1 of the present invention having an internal surface 2, an external surface 3, a length 4 , a width 5 , a height 6, and a thickness (e.g., the thickness of the sheet it is made from) 7. The shell element has a nominal wall thickness 7 of 0.5mm. When a front and a rear shell element encase a notebook computer battery pack and are mated, they form an ignition resistant battery pack enclosure 30. In this example (FIG. 4), the front and rear shell elements are the same molded part.

The shells may accommodate an insert(s) 10 (FIG. 2), such as a structural component, forming a shell/insert construction 20 (FIG. 3A). An insert comprises a frame 11 with a length 12, a width 13, a thickness 14, and a height 15. The insert frame has intersecting divider ribs 16 and 17 which rigidly contain and separate four battery components which make up the battery pack. The insert has one or more boss holes 18 that can be used, for among other things, to affix the insert snugly to the shell 1 or to join a first shell/insert construction 20 to a second shell/insert construction 20.

The shell 1 and insert 10 may be mated by any suitable method, for example using screws, solvent welding, sonic welding, vibrational welding, adhesive materials, i.e., glues, two-sided adhesive tape, snap fits, or combinations thereof. Alternatively, the insert may be affixed to a shell by in-mold adhesion by placing an insert in the thermoform mold then thermoforming the sheet directly to the insert. The insert 10 can be made of any suitable material, for instance it can be plastic (thermoplastic or thermoset) or non-plastic (metal, wood, glass, carbon, etc.). The insert 10 may be made by any suitable method, such as milling, molding, cutting, stamping, forming, or the like. A preferred material for use in the insert 10 is the same type, if not identical, material that the shells are made from. A preferred method to make the insert is by injection molding.

In one embodiment, a boss hole 18 in insert 10 of a first shell/insert construction 20 may comprise a nut 19 which may be fastened by any means, for example a press fit or sonically welded (FIG. 3B). In another embodiment, a screw 31 may pass through the external surface 3 of a second shell/insert construction 20 and through a boss hole 18 in the mated insert 10 for the purpose of screwing into a corresponding nut in a first shell/insert construction 20. Such a screw would be screwed through the external of the shell 1 through the boss hole 18 of its insert 10.

A first and second shell (which may be the same or different) or a first and second shell/insert construction (which may be the same or different), or a first shell and a first shell/insert construction may be combined to form an ignition resistant battery pack enclosure 30 (FIG. 4) of the present invention. The enclosure 30, comprises a first and a second shell element 1 which are mated after encasing the batter pack components. The two shells may be joined by any suitable means, such as those disclosed herein above. After the two shell components encase the battery component and are joined, the encased battery enclosure meets the requirements for a UL 94 V-2, V-l , V-0, and/or 5V rating.

The thickness of the shell is limited by the structural and space requirements of the electronic component application, preferably the shell thickness is between 0.1mm to 1.2mm, preferably 0.5mm to 1.2mm, more preferably 0.2mm to 1mm, more preferably 0.4mm to 1mm, and more preferably of from 0.4mm to 0.8mm.

The example of a battery pack enclosure is for illustration only and it is not intended to limit the scope of the present invention. Moreover, the enclosure of the present invention is not limited for use with only a battery pack, it can be used to encase any electronic devise requiring a thin-walled enclosure, for example, in addition to a battery pack, any hand-held electronic devise, a notebook computer, a laptop computer, an electronic book, a electronic note pad, an office apparatus, a mobile phone, an MP3 player, a MP4 player, a power adapter, a power charger, a storage device, a modem, a GPS, a PDA, an electronic picture frame, and the like. The key fiammability performance criterion for the enclosure of the present invention is to be rated according to the UL 94 Fiammability Standard. The UL 94 fiammability test ratings are based on a test specimens response to several factors based on whether or not a material ignites after being subjected to a Bunsen burner after a specific number of applications each for a specific number of seconds, primarily: burn time, glow time, dripping, and whether or not drips carry flame with them. The UL 94 ratings are: HB, V-2, V-l , V-0, 5VB, and 5VA. The enclosure of the present invention preferably achieves a rating of V-2 or V-l , and more preferably achieves the rating of V-0.

The carbonate polymers employed in the present invention are thermoplastic and are advantageously aromatic carbonate polymers such as the trityl diol carbonates described in USP 3,036,036; 3,036,037; 3,036,038 and 3,036,039; polycarbonates of bis(4- hydroxyphenyl)-alkylidenes (often called bisphenol-A type diols), including their

aromatically and aliphatically substituted derivatives such as disclosed in USP 2,999,835; 3,038,365, 3,334,154, and 4,299,928; and carbonate polymers derived from other aromatic diols such as described in USP 3,169,121 , all of which are hereby incorporated by reference in their entirety.

It is understood, of course, that the carbonate polymer may be derived from (1) two or more different dihydric phenols or (2) one or more dihydric phenols and one or more hydroxy- or acid-terminated reactants such as dicarboxylic acids, or alkylene glycols in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired. The carbonate polymer may be linear, branched, or a combination thereof. Also suitable for the practice of this invention are blends of any one of the above carbonate polymers. Also included in the term "carbonate polymer" are the ester/carbonate copolymers of the types described in USP 4,529,791 ; and 4,677,162; which are hereby incorporated by reference in their entirety. Suitable aromatic polyester carbonates are described in USP 3,169,121 ;

4,156,069; and 4,260,731 ; which are hereby incorporated by reference in their entirety. Of the aforementioned carbonate polymers, the polycarbonates of bisphenol-A and derivatives, including copolycarbonates of bisphenol-A, are preferred. Methods for preparing carbonate polymers for use in the practice of this invention are well known; for example, several suitable methods are disclosed in the aforementioned patents which are hereby incorporated by reference in their entirety. Preferred carbonate polymers have a melt flow rate at 300°C and a load of 1.2 kg of from 3 gram/10 minute (g/10 min) to 30 g/10 min, preferably 3 g/10 min to 10 g/10 min, and more preferably of from 3 g/10 min to 6 g/10 min. The carbonate polymer is greater than 50 percent by weight, preferably equal to or greater than 65 percent by weight, more preferably equal to or greater than 85 percent by weight based on the total carbonate polymer composition.

Phosphates are useful flame retardants for the carbonate polymer composition of the present invention, preferably monophosphates, oligomeric phosphates, or mixtures thereof. A particularly useful monophosphate is triphenyl phosphate. Particularly useful oligomeric phosphates are derived from diphenols, preferred diphenols are diphenylphenol, bisphenol A, resorcinol or hydroquinone or chlorinated or brominated derivatives thereof. A most desirable oligomeric phosphate is "BAPP" which is an oligomeric phosphate flame retardant comprising bisphenol-A bis(diphenyl phosphate) available as REOFOS™ BAPP from Chemtura Corporation. Another desirable high molecular weight phosphate flame retardant is "RDP" which comprises resorcinol (diphenyl phosphate) available as REOFOS RDP from Chemtura Corporation. The phosphorus compounds according to component are known, for example see USP 5,061 ,745; 5,204,394; 5,672,645; 6,596,794; and Re 36,188, all of which are hereby incorporated by reference in their entirety. The phosphorus compounds are present in an amount of from 2 to 20 weight percent, preferably of from 5 to 20 weight percent, and more preferably of from 10 to 15 weight percent based on the weight of the carbonate polymer composition.

High elastic memory polytetrafluoroethylene (PTFE) helps the polycarbonate sample contract upon exposure to a flame source and thus imparts ignition resistance to the polycarbonate. Suitable fluorine containing polymers are those adapted to form a fibril structure to stabilize the polymer under molten conditions. Such polymers are known to include polytetrafluoroethylene, preferably fibrillating polytetrafluoroethylene, a

fluorothermoplast, and/or mixtures thereof, as disclosed by USP 3,005,795; 3,671 ,487; and 4,463, 130, and US Publication No. 20050250908, the teachings of these patents are incorporated herein by reference. The amount of the fibril forming polytetrafluoroethylene is preferably in the range from about 0.1 to about 5 percent and preferably in the range from about 0.3 to about 1.0 percent by weight based on total weight of the carbonate polymer composition.

Optionally, the carbonate polymer composition of the present invention may comprise a second thermoplastic, preferably acrylonitrile, butadiene, and styrene terpolymer (ABS) and/or a polyester. ABS copolymers are well known and many suitable types are commercially available. Either an acrylonitrile-butadiene-styrene or an acrylonitrile- butadiene-alpha-methyl styrene may be used as the ABS component. Nuclear-substituted styrenes, for example p-methylstyrene can also be used. The copolymer can be prepared by free radical polymerization, in particular by emulsion, suspension, solution or bulk polymerization. Useful methods for preparing these copolymers may be found in USP 3,660,535; 3,243,481 ; 4,239,863; and 4,937,285, which are incorporated herein by reference.

Suitable polyester (PES) polymers are thermoplastic polyester polymers, preferably one or more thermoplastic polyalkylene dicarboxylate polymer which are reaction products of aromatic dicarboxylic acids or the reactive derivatives thereof, such as dimethyl esters or anhydrides, and aliphatic, cycloaliphatic or araliphatic diols, dialkyl esters, diacid chlorides, carboxylic acid salts, and diaryl esters, together with mixtures of these reaction products. Preferred polyesters for use in the carbonate polymer compositions of the present invention are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and copolyesters. Also included are the branched copolyesters of poly(l,4-butyl terephthalate) and

poly(ethylene terephthalate). The following patents show the preparation of polyesters and are incorporated by reference, USP 2,465,319; 2,720,502; 2,727,881 ; 2,822,348; 3,047,539; and 3,671 ,487.

If used, preferred amounts of the ABS copolymer and/or polyester are independently from 2 to 25 percent of acrylonitrile, 5 to 20 percent of butadiene, and 10 to 15 percent by weight based on the total weight of the carbonate polymer composition.

Optionally one or more impact modifier, especially core-shell type including methacrylate, butadiene, and styrene core-shell rubbers (MBS), methacrylate, butadiene, and acrylate core-shell rubbers (MBA), and silicon-graft copolymers core-shell rubbers, may be used in the carbonate polymer composition of the present invention in an amount of from 1 to 10 weight percent, preferably of from 2 to 6 weight percent, and more preferable of from 2 to 4 weight percent based on the total weight of the carbonate polymer

composition.

The carbonate polymer compositions of the present invention may further comprise a filler and/or reinforcing material. Preferred fillers, which may also have a reinforcing action, are glass fibers, carbon fibers, metal fibers, metal coated fibers, thermoset fibers, glass beads, mica, silicates, quartz, talc, titanium dioxide, and/or wollastonite alone or in combinations. If present, the filler and/or reinforcing material is present in an amount equal to or greater than about 0.5 percent by weight, preferably equal to or greater than about 5 percent by weight, and more preferably equal to or greater than about 10 percent by weight based on the total weight of the carbonate polymer composition. If present, the filler and/or reinforcing material is present in an amount equal to or less than about 30 percent by weight, and more preferably equal to or less than about 20 percent by weight based on the total weight of the carbonate polymer composition.

In addition, other additives can be included in the modified carbonate polymer composition of the present invention such other types of flame retardants, such as a brominated organic compound, a chlorinated organic compound, or a metal salt; pigments; dyes; antioxidants; heat stabilizers; ultraviolet light absorbers; mold release agents; wax; optical brighteners; and other additives commonly employed in carbonate polymer compositions. Typically, these types of additives are present in an amount equal to or greater than 0.001 weight percent, preferably equal to or greater than 0.01 weight percent, and more preferably equal to or greater than 0.1 weight percent based on the total weight of the carbonate polymer composition. Typically, these types of additives are present in an amount equal to or less than 2 weight percent, preferably equal to or less than 1 weight percent, and more preferably equal to or less than 0.5 weight percent based on the total weight of the carbonate polymer composition.

The carbonate polymer compositions of the present invention are thermoplastic and are suitably prepared by combining the ingredients in effective amounts using any of a variety of blending procedures conventionally employed for thermoplastic polymer blends. For example, dry pellets of the carbonate polymer, and the other additives can be dry blended and the resulting dry blend extruded into the desired shape, they may be extruded into pellets or directly into sheet to be used for thermoforming. By "effective amount" is meant the relative amount of the respective components that is sufficient to provide the desired polymer characteristic.

Processes to provide sheet stock for thermoforming are well known. As mentioned herein above, the carbonate compositions of the invention may in a first step be melt- compounded in a melt-compounding machine (e.g., an extruder) and isolated in a suitable form (e.g., pellets) then in a separate step extruded into sheet. Alternatively, the components of the carbonate compositions of the present invention may be melt- compounded in the sheet producing extruder thus combining melt-compounding and sheet extrusion into a single step process. Sheet extrusion is well known and any method which provides suitable sheet for thermoforming is acceptable. Most processes comprise the steps of melt-compounding in an extruder, extruding the molten thermoplastic melt through a extrusion sheet die having a specific thickness, passing the extruded sheet through a series of rolls for cooling, polishing and regulating final thickness, the extrudate is pulled by pulling rolls and then trimmed and cut into sheet. Optionally, the sheet stock is a multi-layered sheet comprising at least one layer comprising the carbonate composition of the present invention. Other layers may be films for shielding purposes, cosmetic purposes, decoration, scratch and/or mar resistance, soft- touch requirements, and the like.

The formed article of the present invention is manufactured by thermoforming a sheet comprising the abovementioned carbonate polymer composition through the use of conventional machinery employing conventional conditions. There are a number of thermoforming techniques in use, but all are basically variations of two simple processes in which a heated sheet is moved by (1) air in the form of an applied vacuum and/or

pressurized air, or (2) mechanical draw assists which force the sheet into a mold to produce the desired contoured or shaped article. In many cases the two processes are combined to result in a wide variety of procedures to make thermoformed articles. For example, thermoforming methods within the scope of the present invention include, but are not limited to, straight forming, drape forming, snapback forming, reverse-draw forming, plug- assist forming, plug-assist/reverse draw forming, air-slip forming/plug-assist, air-slip forming, matched tool forming, twin-sheet forming, and the like.

The thermoforming process includes heating a sheet until it softens or starts to sag, after which one or more of vacuum, air pressure, and/or mechanical draw assist is applied and the heated sheet is drawn into a female mold, sometimes referred to as die, drawn over a male mold, or the two molds are used together to form an article, the formed article is cooled, removed from the mold, and trimmed as necessary.

Preferably the thermoforming process is a high pressure thermoforming process and utilizes a pressure up to 150 bar from an aero-compressor and/or heating via IR heat sources. Both pressure and IR heating help to ensure precise dimensional forming of the molded part.

The sheet temperature for thermoforming a sheet of the carbonate polymer of the present invention is less than or equal to about 300°C, preferably less than or equal to about 325°C and more preferably less than or equal to about 350°C. Further, the sheet

temperature for thermoforming a sheet of the carbonate polymer of the present invention is greater than or equal to about 450°C, preferably greater than or equal to about 425°C and more preferably greater than or equal to about 400°C.

The thermoformed shell has an internal surface and an external surface. Either surface independently may be smooth or textured or a combination thereof. Further, a logo or some other such mark may be molded into the surface. The carbonate composition and process to make the ignition resistant electronic component enclosure of the present invention reduces and can even eliminate the material deterioration due to high temperature/high shear rate in conventional injection molding processes. Further, surface defects are reduced or even eliminate, for example welding lines, silver streaks, jet marks and material burn marks which are commonly generated during the injection molding process. Further, ignition resistant electronic component enclosure of the present invention potentially affords improved environmental stress crack resistance (ESCR) for better chemical resistance because a high molecular weight carbonate polymer is used thus avoiding the brittleness from conventional easy flow, low molecular weight carbonate polymers required for injection molding.

EXAMPLES

The compositions of Examples 1 to 8 are shown is Table 1 and the amounts are given in parts by weight based on the total weight of the carbonate composition. The components are melt compounded in a Century CX-40 twin screw co-rotating extruder. The extruder screw speed is 250 rotations per minute (RPM), vacuum is 50 millimeter mercury (mm-Hg), and the output is about 60 kilogram per hour (kg/hr). The temperature profile from the hopper to the nozzle is 260°C, 270°C, 280°C, 285°°C, 285°C, 280°C, 275°C, 275°C, and 275°C. Prior to compounding, the polycarbonate is dried for at least 4 hours at 120°C. Powdered materials are dry blended together. A three feeder system is used: the polycarbonate is fed via one feeder, impact modifier and powdered additives are added as a dry blend via a second feeder, and the phosphate flame retardant is added at 80°C via a liquid third feeder. The extrudate is cooled in a 50°C water bath and commuted to pellets.

In Table 1 :

"PC-1" is a linear bisphenol-A polycarbonate homopolymer having a melt flow rate (MFR) of about 4.3 grams per 10 minutes (g/10 min) which corresponds to weight average molecular weight (Mw) of about 34,000 grams per mole (g/mole);

"PC-2" is a linear bisphenol-A polycarbonate homopolymer having a MFR of about

15 g/10 min which corresponds to a Mw of about 25,000 g/mole;

"PC-3" is a linear bisphenol-A polycarbonate homopolymer having a MFR of about 30 g/10 min which corresponds to a Mw of about 21 ,000 g/mole; "IM" is an impact modifier comprising a methacrylate, butadiene, and acrylate core-shell rubber available as PARALOID EXL 2602 from the Dow Chemical Company;

"BAPP" is an oligomeric phosphate flame retardant comprising bisphenol-A bis(diphenyl phosphate) available from Chan-Chun Plastic Co.;

"RDXP" is resorcinol dixylenyl phosphate a flame retardant additive with the following structure:

available from Daihachi;

"PTFE" is an anti-drip agent comprising a fibril forming polytetrafluoroethylene available from DuPont;

"PETS" pentaerythritol tetrastearate and is available from Shinkong Synthetic Fiber Corporation of Taiwan., Ltd.; and

"IRGANOX" is a phosphite antioxidant available as IRGANOX™ B-900 from Ciba Specialty Chemicals.

The pellets are dried for at least 4 hours at 120°C then extruded into 0.5mm sheet using a Wu-Hang SB-450 45 mm screw (L D: 30/1) co-extruder extruder. The following is the hopper temperature: 120°C, and barrel temperatures: 270°C, 280°C, 285°C, and 280°C. All roll temperatures set points are 100°C. The extruded sheet measured 2 meter (m) long by lm wide by 0.5mm thick.

The following test properties for the extruded sheet are reported in Table 1 :

"MFR" is melt flow rate of the polymer determined according to ASTM D 1238 under conditions of 300°C and a load of 1.2 kilograms (300°C/1.2 kg) and is reported in g/10 min;

"Izod" is notched Izod impact and is determined according to ASTM D 256 wherein the test specimen has a notch with a 10 mil radius in the center of the test bar and the test specimens are conditioned for a minimum of 24 hours at 23°C and 70 percent relative humidity prior to testing. An Atlas impact tester is used with a 2 joule impact at ambient temperature; and

"UL 94" flammability ratings are determined in accordance with Underwriter's Laboratories' Standard 94, whether or not the sample had flaming drips, the total burn time (Burn-r) in seconds (sec), and its UL 94 rating are listed.

Table 1

Example 9 is an ignition resistant housing of the present invention comprising the sheet of Example 5 which is thermoformed into a shell element 1 measuring 260mm by 133mm by 2mm. The thermoforming machine is an HPFM 250A manual feed

thermoformer manufactured by V-Link, Ltd., equipped with two sided heating. The infra red heating elements are set to from 300°C to 320°C and the sheet is heated to a temperature of about 120°C. Sheet heating cycle dwell times range from about 60 seconds to 70 seconds. The upper mold temperature is 95°C with a lower mold temperature of 90°C. A vacuum of about 75 centimeter of mercury is achieved. Example 9 further comprises an insert 10 which is injection molded from the pellets of the carbonate composition of Example 5 using a 220MT injection molding machine. Barrel temperatures are from 240°C to 265°C, clamp pressure is 140 bar, cooling time is 15 seconds, with an over all cycle time of 45 seconds. The insert comprises a frame measuring 258.6mm by 132mm by a height of 1.5mm comprising bosses, and ribs and fits within the shell element. The frame is 3.6mm thick.

One insert 10 is ultrasonically welded to one shell element 1 to form a shell/insert construction 20 using a 4200W welder available form Yi Yuan with a pressure of 4 bar and a delay time of about 0.7 second, a welding time of about 0.6 seconds, and a cooling time of about 0.5 seconds.

Two shell/insert constructions 20 form the top and a bottom for the ignition resistant battery pack enclosure 30. The ignition resistant battery pack enclosure 30 is completed by inserting the batter pack components into a first (e.g., bottom) shell/insert construction 20 and assembling a second (e.g., top) shell/insert component 20 thereto using four screws, one in each corner.

The battery pack enclosure 30 achieves a UL 94 V-0 rating.

The mechanical strength of the ignition resistant battery pack enclosure is assessed by an industry Drop Test which comprises:

(1) Dropping a battery on the ground at the four corners from a specific height. (2) After four droppings, check structure of the battery enclosure.

(3) If there are no visible cracks, the enclosure passes the test, if there are any visible cracks, the enclosure fails the test.

Example 9 passes the drop test from lm and from 1.5m. For comparison, a commercially available battery pack of comparable weight and comprising a shell having comparable dimensions and the same shell wall thickness as enclosure of Example 9 passes the drop test at 1.0m height but, fails at 1.5m. The commercial battery pack enclosure is made by the conventional process of injection molding, a very high flow polymer is required to fill the 0.5mm part. The means to achieve high flow (i.e., low molecular weight carbonate polymer) result in poor mechanical strength, specifically brittleness.