Description

Light source having fluoropolymer outer layer Technical Field

[0001] The invention pertains to a light source having a fluoropolymer outer layer and to a process for its manufacture.

Background Art

[0002] The present invention relates generally to light sources having shatterable encasement means.

[0003] Light sources generally comprise a light emitting element comprised within encasement means which are generally made from translucent materials such as glass, quartz and the like. Among well-known light sources, mention can be notably made of electric lamps, such as incandescent lamps, vapor lamps (sodium vapor lamps, mercury vapor lamps, etc.), arc lamps, fluorescent lamps, ultraviolet lamps, etc. These electric lamps typically have at least one base which provides structural support for the lamp and which also provides positive, negative, and grounding contacts for electrical power. A filament, or light source, which converts electrical energy to light is connected between the contacts. The filament is generally encased in a translucent encasement which protects the filament from the surrounding environment and contains the gaseous vapors, vacuum, etc. surrounding the filament and needed for the electric lamp to operate properly. The encasement is usually a translucent glass or quartz container, such as a light bulb or a glass tube.

[0004] However, the remote possibility of a dispersion of glass shards resulting from a fracture of said encasement cannot be substantially avoided: although occurrence of such a fracture is rare, it could nevertheless represent a safety hazard to persons or objects in the immediate vicinity of the light source and may be a potential source of contamination in particularly sensitive environments (i.e. in medical context, e.g. in operating theatres, in food handling and the like).

[0005] Methods have been suggested in the past to improve the ability of incandescent lamp, tungsten-halogen and arc discharge lamps to withstand a fracture of shatterable encasement means.

[0006] A solution which has been proposed is the practice of applying a coating on the outside surface of the light source envelope to hold the shatterable material pieces together upon envelope breakage due e.g. to an impact by an external force. Said containment coating should be relatively transparent so as to allow a substantial amount of light to pass though it, and so as not to affect light source efficiency. In addition said coating should be resistant to degradation by high temperature and/or ultraviolet radiation. Finally, it should provide the required mechanical resistance and tensile strength so as to withstand impact and puncture by e.g. glass shards.

[0007] Materials which have been proposed in the past are basically silicone-based or fluoropolymer-based.

[0008] Thus, US 3715232 (GTE SYLVANIA INC ) 06.02.1973 discloses an electric lamp having a glass envelope with a tacky, shatter-resistant silicone rubber coating over the envelope and a coating over this latter of a hard, heat resistant silicone material to resist the accumulation of dust on the tacky coating.

[0009] Also, US 6501219 (GENERAL ELECTRIC COMPANY) 31.12.2002 discloses an incandescent lamp exhibiting improved impact resistance comprising a coating of a heat-curable, platinum catalyzed, silicone coating composition comprising a vinyl containing polydimethylsiloxane fluid, a siloxane hydride and a vinyl resin comprising trimethylsiloxy units and SiO ₂ units.

[0010] Nevertheless, coatings based on silicone rubber suffer from the drawback that they require complex application technologies and curing treatment. Moreover, their intrinsic tackiness promotes accumulation of dust unless additional measures are taken, e.g. over-coating with a non-sticky material.

[0011] In this view, fluoromaterials possessing intrinsic anti-sticky and surface release properties are advantageous over silicone rubber coating.

[0012] In this field, CA 1243723 (GTE PRODUCTS CORPORATION) 25.10.1988 discloses an electric lamp having an envelope, a light-source capsule mounted within the envelope and a containment coating. The containment

coating, which is disposed substantially over the outer envelope, has the capability of preserving the integrity of the envelope from piercing, due to shard dispersion from the light-source capsule, in the unlikely event that the capsule should fracture. As examples of suitable containment coating materials mention is made of TEFLON ^® PFA (perfluoroalkoxy) resins, fluorinated ethylene-propylene (FEP) resins and of polychlorotrifluoroethylene (PCTFE) resins.

[0013] Nevertheless, said resins possess relatively low transmittance, both in the visible and, in particular, in the near UV region.

[0014] There is thus still a need in the art for light sources having shatterable encasement means comprising an outer layer having outstanding transparency both in the visible and UV region, UV stability (no discolour), no age and lower haze value, and still possessing adequate thermal resistance (the material being unaffected by prolonged exposure to continuous high operating temperature), and also maintaining adequate mechanical resistance and tensile strength so as to withstand impact and puncture by e.g. glass shards. Moreover, for instance for light sources having lower operating temperatures and/or for next generation low energy consumption light sources having plastic components, there is a need for materials for outer layers which fulfil all above requirements and which can be, in addition, processed at low temperatures.

Disclosure of Invention

[0015] The Applicant has now surprisingly found that these and other needs can be achieved by providing a light source having shatterable encasement means comprising an outer layer comprising a tetrafluoroethylene (TFE) polymer [polymer (F)], said polymer (F) comprising:

- recurring units derived from TFE; and

- from 6.5 to 35 % wt of recurring units derived from at least one perfluoromonomer [monomer (CM)] chosen among:

(i) perfluoroalkylvinylethers complying with formula CF ₂ =CFOR _f1 , in which R _f1 is a C ₁ -C ₆ perfluoroalkyl, e.g. -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ and/or (ii) perfluoro-oxyalkylvinylethers complying with formula CF ₂ =CFOX ₀ , in which X ₀ is a C ₁ -C ₁₂ perfluorooxyalkyl having one or more ether groups,

like perfluoro-2-propoxy-propyl; and (iii) mixtures thereof.

[0016] Thanks to the use as outer layer of a fluoropolymer like polymer (F) possessing outstanding thermal resistance and mechanical strength, the light source is efficiently protected against accidental fracture of the shatterable encasement means with practically no loss in lighting efficiency nor in prolonged use or exposure to UV light.

[0017] The invention also pertains to a process for manufacturing the light source having shatterable encasement means comprising the outer layer comprising polymer (F) as above described.

[0018] The light source having shatterable encasement means may be of all suitable configurations and types.

[0019] Shatterable encasement means of the light source of the invention generally consist essentially of glass and/or quartz, even if other transparent shatterable encasement means materials can still be used to the purposes of the invention.

[0020] To the purpose of the invention, the term glass is intended to denote an amorphous inorganic product of fusion comprising silicon dioxide that has cooled to a rigid condition without crystallizing.

[0021] Among suitable glasses for the shatterable encasement means of the invention, mention can be notably made of alkali-metal and alkaline-earth silicate, borosilicate, aluminosilicate, lead silicate glasses.

[0022] The light source can be virtually any type of electrical lamp having shatterable encasement means, including gas discharge lamps (e.g. fluorescent lamps, ultraviolet lamps, arc lamps), incandescent lamps, and the like.

[0023] An incandescent lamp is a source of light wherein an electrical current passes through a thin filament, heating it and causing it to become excited, releasing thermally equilibrated photons in the process. The enclosing encasement bulb prevents the oxygen in air from reaching the hot filament, which otherwise would be destroyed rapidly by oxidation. Encasement means of an incandescent lamp may be pear-shaped, like a standard incandescent bulb, wedge-shaped, trapezoidally-shaped,

tube-shaped, or take virtually any shape which may be used to encase above mentioned filaments. Generally encasement means of an incandescent lamp are essentially made of glass.

[0024] Gas discharge lamps are a family of artificial light sources that generate light by sending an electrical discharge through an ionized gas, i.e. a plasma. Typically, such lamps use a noble gas (argon, neon, krypton and xenon) or a mixture of these gases. Most lamps are filled with additional materials, like mercury, sodium, and/or metal halides. In operations, the gas is ionized, and free electrons, accelerated by the electrical field in the tube, collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation. Ultraviolet radiation is converted to visible light by a fluorescent coating on the inside of the lamp's glass surface for some lamp types, wherein primary light emission occurs in the UV region.

[0025] The fluorescent lamp is the best known gas discharge lamp, wherein the short-wave ultraviolet light emitted by a mercury vapour in neon or argon gas causes a phosphor deposited on the inner surface of the encasement means to fluoresce, producing visible light.

[0026] UV lamps are based on the same phenomena but no phosphor at all is used.

[0027] Generally, the encasement means of gas discharge lamps containing the required gas and/or other components are made from glass (e.g. soda lime glass, borosilicate glass and the like) or quartz. Quartz is required for UV lamps, thanks to its improved transparency in this region.

[0028] Encasement means of gas discharge lamps are generally under the form of tubes, either straight tubes or folded arrays of tubes, having either at one or at both ends electrical contact means.

[0029] According to a preferred embodiment of the invention the light source is a gas discharge lamp, wherein the encasement means consist of a glass or quartz tube, preferably a glass tube.

[0030] It is understood that the outer layer of the light source of the invention may

cover the entirety of the shatterable encasement means surface or it may cover only a part of said surface. Generally, the outer layer of polymer (F) will cover an essential part of the shatterable encasement means surface.

[0031] The outer layer of the light source of the invention can comprise, in addition to polymer (F), additional components, e.g. thermoplastic polymer components and/or typical polymer (F) additives, fillers and the like.

[0032] Nevertheless, it is preferred that these additional components do not substantially interfere with target properties of outer layer of polymer (F). Thus, in preferred embodiments of the invention, outer layer consists essentially of polymer (F).

[0033] In polymer (F) as above defined, monomer (CM) is preferably selected among perfluoroalkylvinylethers complying with formula CF ₂ =CFOR _f1 , in which R _f1 is a C ₁ -C ₆ perfluoroalkyl, more preferably a C ₁ -C ₃ perfluoroalkyl

[0034] Monomer (CM) is more preferably selected among perfluoroalkylvinylethers complying with formula CF ₂ =CFOR _fr , in which R tr is -CF ₃ (MVE), -C ₂ F ₅ (EVE), or -C ₃ F ₇ (PVE), or mixtures thereof.

[0035] Monomer (CM) is most preferably CF ₂ =CFOCF ₃ (MVE).

[0036] Preferably polymer (F) of the invention is free from recurring units other from those derived from TFE and comonomers (i) and/or (ii) as above detailed.

[0037] Thus, polymer (F) preferably consists essentially of:

- recurring units derived from TFE; and

- from 6.5 to 35 % wt of recurring units derived from a monomer (CM) chosen among:

(i) perfluoroalkylvinylethers complying with formula CF ₂ =CFOR _f1 , in which R _f1 is a C ₁ -C ₆ perfluoroalkyl, preferably a C ₁ -C ₃ perfluoroalkyl, e.g. -CF ₃ , -C 2F ₅ , -C ₃ F ₇ and/or

(ii) perfluoro-oxyalkylvinylethers complying with formula CF ₂ =CFOX ₀ , in which X ₀ is a C ₁ -C ₁₂ perfluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxy-propyl; and (iii) mixtures thereof.

[0038] The term "consisting essentially of is understood to mean that the polymer chain is essentially made of recurring units as above detailed. Moieties like

end-groups, chain defects, entities derived from other polymerization ingredients like initiators, chain transfer agents can be nevertheless present in polymer (F).

[0039] Polymer (F) is advantageously semi-crystalline.

[0040] The term semi-crystalline is intended to denote a polymer (F) which possesses a detectable melting point. It is generally understood that a semi-crystalline polymer (F) possesses a heat of fusion determined according to ASTM D 3418 of advantageously at least 0.4 J/g, preferably of at least 0.5 J/g, more preferably of at least 1 J/g.

[0041] Semi-crystalline polymers (F) have significant advantages over amorphous products, as they exhibit the required properties, and in particular suitable mechanical properties without additional crosslinking treatments.

[0042] Excellent results were obtained when polymer (F) had a heat of second fusion (δH ^f ) of 27 to 2 J/g, preferably of 26 to 3 J/g, most preferably of 24 to 4 J/g. Polymers (F) complying with such requirement were found to well behave as outer layer in light sources having shatterable encasement means, as they advantageously possess at the same time:

- suitable mechanical resistance (in particular stress at break);

- optical properties (very high transparency from UV to IR region with visible light transmittance as high as about 99 %) and low Haze values;

- thermal resistance to degradation by high temperature (unchanged MFI for long residence time and very low weight loss at high temperature in TGA analysis) and/or by ultraviolet radiation, but also

- outstanding surface properties (smoothness and release capabilities). [0043] In addition, polymer (F) can be chosen so as to provide materials having low melting point so as to be processed at lower temperatures: these materials can be used with success for the assembly of light sources comprising, inter alia, plastic components sensitive to temperature. [0044] Moreover, light sources having shatterable encasement means comprising outer layer of polymer (F) can be advantageously produced at higher throughput rates or with reduced energy consumption, as polymer (F) offer improved mechanical & optical properties/processability compromise moving from low MFI (1-5) to medium MFI (5 - 9), high MFI (10-30) and

very high MFI (30-60). [0045] MFI of polymer (F) is not particularly limited. Generally, polymer (F) possesses a MFI of 1 to 100 g/10 min, when measured according to

ASTM D 1238 standard. [0046] Appropriate MFI of polymer (F) will be chosen by the skilled in the art as a function, notably, of the processing technique and/or of the required performances. [0047] It is essential for polymer (F) to have an amount of recurring units derived from monomer (CM) comprised from 6.5 to 35 % wt. [0048] When the polymer (F) comprises less than 6.5 % wt of recurring units derived from monomer (CM), its optical properties are poor and material lacks of suitable transparency. [0049] When polymer (F) comprises more than 35% wt of recurring units derived from monomer (CM), its continuous service temperature rating decreases too much to provide for suitable protection against shattering of the encasement means of the light source; also mechanical properties become unsatisfactory. [0050] Polymer (F) comprises at least 6.5 %, preferably at least 7 %, more preferably at least 7.5 % by weight of recurring units derived from monomer (CM). [0051] Polymer (F) comprises at most 35 %, preferably at most 33%, more preferably at most 30% by weight of recurring units derived from monomer

(CM). [0052] Polymer (F) advantageously possesses a melting point (T _m2 ) from 130°C to 280 ⁰ C, measured according to ASTM D 3418. [0053] According to a first embodiment of the invention, polymer (F) possesses a melting point (T _m2 ) from 230 ⁰ C to 280°C, measured according to ASTM D

3418. Light sources according to this first embodiment of the invention are advantageously well-suited to sustain high continuous operating temperatures (typically of up to T _m2 - 30°). [0054] Polymer (F) according to this first embodiment of the invention comprises from 6.5 to 20, preferably from 7.0 to 15, more preferably from 7.5 to 12 % by weight of recurring units derived from monomer (CM).

[0055] Excellent results for this embodiment have been obtained with a polymer (F) comprising from 8 to 11 % wt of recurring units derived from MVE.

[0056] According to a second embodiment of the invention, polymer (F) possesses a melting point (T _m2 ) from 130°C to 230°C, measured according to ASTM D 3418. Light sources according to this second embodiment of the invention are well-suited to sustain lower continuous operating temperatures (typically of up to T _m2 - 30°C), and can be produced with success at lower processing temperatures.

[0057] Polymer (F) according to this second embodiment of the invention comprises from 20 to 35, preferably from 22 to 33, more preferably from 24 to 30 % by weight of recurring units derived from monomer (CM).

[0058] Excellent results for this embodiment have been obtained with a polymer (F) comprising from 25 to 30 % wt of recurring units derived from MVE.

[0059] The outer surface of the light source is from about 5 to about 1000 micrometers thick, preferably about 15 to about 500 micrometers thick.

[0060] The invention also pertains to a process for manufacturing the light source having shatterable encasement means comprising the outer layer comprising polymer (F) as above described.

[0061] The process of the invention comprises advantageously coating the shatterable encasement means of the light source with the outer layer comprising polymer (F).

[0062] The outer polymer (F) layer can be coated on the light source having shatterable encasement means using any suitable known manner. Typical techniques for coating polymer (F) on the shatterable encasement means of the light source include liquid and dry powder spray coating, dip coating, wire wound rod coating, fluidized bed coating, powder coating, electrostatic spraying, sonic spraying, blade coating, casting, co-extruding, extruding and shrinking pre-formed shrinkable tubes, extruding and welding pre-formed films, sheets, sleeve and shrinkable tubes (also called roll covers), and the like.

[0063] The process of the invention can be carried out using either a pre-formed film comprising polymer (F) as a precursor of the outer layer or forming said layer directly from polymer (F), e.g. from powder.

[0064] According to a first embodiment of the invention, the process of the invention comprises assembling the outer layer comprising polymer (F) by introduction of the light source having shatterable encasement means in a shrinkable pre-formed tube comprising (preferably consisting essentially of) polymer (F), and, subsequently, submitting said assembly to heat treatment to cause shrinkage of said tube onto said shatterable encasement means of the light source.

[0065] The process according to this first embodiment of the invention is particularly adapted to light sources having shatterable encasement means under the form of tubes.

[0066] According to a second embodiment of the invention, the process of the invention comprises co-extruding from the melt the outer layer comprising polymer (F) and the encasement means so as to directly obtain a light source having shatterable encasement means comprising an outer layer comprising polymer (F).

[0067] The process according to this second embodiment of the invention is particularly adapted to light source having shatterable encasement means under the form of tube, wherein the encasement means are made from a thermoprocessable composition which can be co-extruded with polymer (F).

[0068] According to a third embodiment of the invention, the process advantageously comprises the following steps: (i) providing a light source having shatterable encasement means; (ii) optionally heating said shatterable encasement means at a temperature exceeding melting point (T _m2 ) of polymer (F); (iii) spraying the surface of the shatterable encasement means with a composition (C) comprising polymer (F) so as to homogeneously coat at least part of the shatterable encasement means; (iv) optionally heating the so-coated shatterable encasement means at a temperature exceeding melting point (T _m2 ) of polymer (F), with the provisio that the process comprises at least one of step (ii) and (iv).

[0069] Generally, the process according to this third embodiment of the invention

comprises at least one step (iv) as above detailed (so-called "baking" step), while spraying can be realized either on heated or non-heated surface of the shatterable encasement means.

[0070] It is also generally preferred, in particular when shatterable encasement means are made of glass, that a controlled cooling follow the baking step (iv), so as to avoid thermal shocks and release internal tensions in the glass shatterable encasement means.

[0071] Composition (C) can be a dry or a wet composition.

[0072] Standard techniques well known to those skilled in the art will be suitable for this second embodiment of the invention.

[0073] Among the various standard techniques, those employing polymer dispersions in organic solvents or their aqueous latices and the electrostatic powder coating (EPC) can be mentioned.

[0074] Should the composition (C) be a wet composition, various conventional coating methods may be employed. Examples are dipping method, spray method, roll coat method, doctor blade method and flow coat method.

[0075] Should the composition (C) be a dry composition, the electrostatic powder coating (EPC) method, wherein the particles of composition (C) are electrostatically charged and deposited on the earthed surfaces of the shatterable encasement means, have acquired a remarkable importance.

[0076] Optionally, any known and available suitable adhesive layer may be positioned between the outer layer and the substrate.

[0077] The present invention will be described in more detail with reference to the following examples whose purpose is merely illustrative and not limitative of the scope of the invention.

[0078] Example 1 - Manufacture of polymer (F) samples

[0079] POLYMERIZATION RUNS

[0080] Polymer (F-1) (TFE/MVE 94.7/5.3 (molar ratio) (91.8/8.3 by nominal weight))

[0081] In a 22 litres AISI 316 steel vertical autoclave equipped with baffles, and stirrer working at 400 rpm, were introduced 13.9 litres of demineralized water, 160 g of a microemulsion prepared according to US 4864006 (AUSIMONT SPA ) 05.09.1989 . Then the temperature was raised to the

reaction temperature of 75°C; once this set point temperature achieved, 0.37 absolute bars of ethane and 4.02 absolute bars of perfluoro methylvinylether were introduced. A gaseous mixture of TFE/MVE in a molar nominal ratio of 94.7/5.3 was added until reaching a pressure of 21 absolute Bars.

[0082] The composition of the gaseous mixture present in the autoclave head-space was analyzed by gas chromatography (G. C). Before starting polymerization, the gaseous phase was found to consist of (molar percentages): 76.6 % TFE, 22.4 % MVE and about 1 % Ethane. 225 ml of a potassium persulphate (KPS) 0.0296 M solution were then fed to start the polymerization.

[0083] The polymerization pressure was maintained constant by feeding the above mentioned monomeric mixture; when 8800 g of the mixture have been fed, feeding was interrupted and while maintaing reaction mixture at the set point temperature, the pressure was enabled to decrease down to 9 absolute bars. Then the reactor was cooled to room temperature, the latex was recovered and coagulated with HNO ₃ (65% by weight). The polymer was then washed with demineralized water and dried at 220°C. So obtained powder was then pelletized.

[0084] Table 1 here below summarizes compositions and melting properties of several polymer (F) samples, and, to the sake of comparison, corresponding properties of selected commercially available fluoropolymer samples, which have been used in the past for this application.

[0085] Polymer (F-2) (TFE/MVE 94.8/5.2 (molar ratio) (91.65/8.35 nominal weight ratio))

[0086] Same procedure as for polymer (F-1) was repeated, but using:

- a gas mixture TFE/MVE (94.8/5.2 mol/mol)

- an ethane initial partial pressure of 0.26 absolute Bars.

- an initial MVE partial pressure of 4 absolute Bars;

- an amount of KPS solution 0.0148 M of 125 ml.

[0087] The gaseous phase before starting polymerization was found by G. C. to consist of (molar percentages): 77.5% TFE, 21.7% MVE and about 0.8% Ethane.

[0088] Polymer (F-3) (TFE/MVE 95/5 (molar ratio) (91.95/8.05 nominal weight ratio))

[0089] Same procedure as for polymer (F-1) was repeated, but using:

- a gas mixture TFE/MVE (95/5 mol/mol)

- an ethane initial partial pressure of 0.22 absolute Bars.

- an initial MVE partial pressure of 3.8 absolute Bars;

- an amount of microemulsion of 136 g;

- an amount of KPS solution 0.0296 M of 110 ml.

[0090] The gaseous phase before starting polymerization was found by G. C. to consist of (molar percentages): 74.3% TFE, 25% MVE and about 0.7% Ethane.

[0091] Polymer (F-4) (TFE/MVE 93.9/6.1 (molar ratio) (90.35/9.75 nominal weight ratio))

[0092] Same procedure as for polymer (F-1) was repeated, but using:

- a gas mixture TFE/MVE (93.9/6.1 mol/mol)

- an ethane initial partial pressure of 0.23 absolute Bars.

- an initial MVE partial pressure of 5.2 absolute Bars;

- an amount of microemulsion of 136 g;

- an amount of KPS solution 0.0296 M of 110 ml.

[0093] The gaseous phase before starting polymerization was found by G. C. to consist of (molar percentages): 69% TFE, 30.4% MVE and about 0.6%

Ethane. [0094] Polymer (F-5) (TFE/MVE 90/10 (molar ratio) (84.4/15.6 nominal weight ratio)) [0095] Same procedure as for polymer (F-1) was repeated, but using an autoclave having an inner volume of 5 litres, equipped with a stirrer operating at 650 rpm, and:

- a gas mixture TFE/MVE (90/10 mol/mol)

- an ethane initial partial pressure of 0.4 absolute Bars.

- an initial MVE partial pressure of 7.4 absolute Bars;

- an amount of microemulsion of 25 g;

- an amount of KPS solution 0.054 M of 70 ml.

[0096] The gaseous phase before starting polymerization was found by G. C. to

consist of (molar percentages): 64% TFE, 35% MVE and about 1 % Ethane.

[0097] Polymer (F-6) (TFE/MVE 80/20 (molar ratio) (70.5/29.5 nominal weight ratio))

[0098] Same procedure as for polymer (F-1) was repeated, but using:

- a gas mixture TFE/MVE (80/20 mol/mol)

- an ethane initial partial pressure of 0.09 absolute Bars.

- an initial MVE partial pressure of 8.8 absolute Bars;

- an amount of microemulsion of 136 g;

- an amount of KPS solution 0.0103 M of 170 ml.

[0099] The gaseous phase before starting polymerization was found by G. C. to consist of (molar percentages): 52.6% TFE, 47.3% MVE and about 0.1 % Ethane.

[0100] Table 1 here below summarizes compositions and melting properties of polymer (F-1) to (F-6) as above detailed, and, to the sake of comparison, corresponding properties of selected commercially available fluoropolymer materials, which have been used in the past for this application. Hexafluoropropylene (HFP) and EVE content in prior art material has been determined according to the method described in US 5677404 (DU PONT) 14.10.1997 . PVE content was determined according to an internal IR method, measuring optical densities of spectral bands centred at 995 cm ^"1 and 2365 cm ^"1 , according to the following formula:

PVE (% wt) = ' ^{995 cm 1} x 0.99

2365 cm ¹

[0101]

Table 1

[0102] ^* MFI of polymer (F-5) was determined also at lower temperature: MFI (275°C/2,16kg) = 4.7 g/10 min

[0103] Polymers listed in table 1 here above were processed for yielding pellets by extrusion on a twin screw extruder (Braebender).

[0104] Table 2 here below draws a comparison between mechanical properties and optical properties of polymers as above described, as determined on specimens punched out from moulded film.

[0105] Flex-life was determined on compression moulded film having thickness 0.3 mm according to ASTM D 2176 standard.

[0106] Stress at break was measured on specimen obtained by a compression moulded plaques having a thickness 1.5 mm and following the ASTM D 638 standard.

[0107] Haze was determined on plaques obtained by compression moulded having a thickness of 1.8 mm according to ASTM D 1003 standard. The sample was placed on a glass cell filled with water to eliminate the contribution arising from the scattering due to the surface roughness. As a reminder, haze is the percentage of the transmitted light that, in passing through a specimen, deviates from incident beam by light scattering. Only light flux deviating more than 2.5° on the average is considered to be haze.

[0108] Trasmittance (%) was determined on slab specimens obtained by compression moulded, said speciments being polished to a mirror-like

finishing; said specimens have been obtained by polishing with thin sand paper and finally with an alumina slurry in water the film obtained by compression moulding. UV-Vis spectra (200-800 nm) have been recorded with a Perkin Elmer Lambda 2 double beam spectrophotometer. Raw data obtained have been normalised to a unique thickness of 0.5 mm (500 microns) and compared.

[0109]

Table 2

[0110] n.a. = not available

[01 1 1] MFI stability test

[0112] Sample (F-2) was submitted to a MFI stability test, by determining its melt flow index according to ASTM D 1238 and carrying out MFI determination elsewhere according to said standard but after having maintained the sample during 60' at 372°C in the loading chamber of the MFI apparatus. In both cases, a MFI value of 8 g/10 min was measured. These results

suggest that no molecular weight change/degradation is observed even after prolonged treatment at high temperature.

[01 13] Thermal stability test via thermogravimetrical analysis (TGA) [01 14] Sample (F-1) and comparative sample TEFLON ^® FEP G were submitted to TGA analysis in dynamical mode according to ISO 7111 method under nitrogen atmosphere and the temperature required for obtaining a weight loss of, respectively, 1 % wt and 2% wt was measured. Data embedded in

Table 3 here below well demonstrate improved thermal stability of polymer

(F) compared to materials of prior art, as the target weight loss is achieved at higher temperature.

[01 15]

Table 3

[01 16] [01 17] Data summarized in tables 2 and 3 here above well demonstrate that polymers (F) possess outstanding optical properties while maintaining satisfactory mechanical behaviour (stress at break and flex life), so that they can be advantageously used for manufacturing outer layer of light source having shatterable encasement means. Due to their improved processability/mechanical propertied compromise, it is also possible to manufacture said parts with higher throughput or substantial energy savings.

[01 18] Example 2 - Assembling a light source having shatterable encasement means comprising an outer layer of polymer (F-3)

Polymer (F-3) as above described is extruded to yield a heat shrinkable tubing that has been expanded mechanically to slide over a fluorescent soda lime glass tube lamp. The heat shrinkable tubing diameter is selected so as it easily slips over the lamp tube length insuring that it will shrink to the tube diameter.

[01 19] The lamp tube is introduced in polymer (F-3) tubing and then heated to shrink down to a tight fit that will not fall off. To insure a smooth, uniform

covering without wrinkles, hot air guns are used for uniformly heating the assembly while rotating the lamp tube at a fairly uniform speed. The outer layer of polymer (F-3) is finally allowed to slowly cool. So obtained assembly comprising an outer layer of polymer (F-3) is tested for its shatter resistance. The coating of polymer (F-3) reliably contains the glass fragments of the purposely fractured lamp tube.

[0120] Example 3 - Assembling a light source having shatterable encasement means comprising an outer layer of polymer (F-1)

[0121] Polymer (F-1) as above detailed in powder form was applied by electrostatic powder coating on a glass lamp so as to obtain an outer layer having a thickness of about 30 μm. Baking of the above mentioned coated assembly was performed in a oven at a temperature of 360°C. A controlled cooling down to room temperature followed. The surface of the outer layer of polymer (F) was found to be smooth. The outer layer of polymer (F-1) was found to reliably contain the glass fragments of the purposely fractured glass lamp.