Covers for LED light sources

Abstract

The invention relates to the use of branched aliphatic hydrocarbons such as squalane in compositions based on thermoplastic polymer, in particular on polycarbonate, which are used for producing molded parts used in LED lighting units, such as covers for instance. According to the invention it has been found that the use of branched aliphatic hydrocarbons makes it possible to enhance the total transmission and the transmission in the range from 360 to 460 nm, thus making corresponding compositions particularly suitable for producing molded parts for use in combination with white LED light sources. It has additionally been shown that yellowing and haze are simultaneously reduced.

Claims

1. An LED illumination unit comprising an LED light source having a peak wavelength in the range from 360 to 460 nm and a molded part made of a transparent or translucent thermoplastic composition containing a) thermoplastic polymer, wherein aromatic polycarbonate is present as thermoplastic polymer, b) 10-2500 ppm of one or more phosphorus-based stabilizers, selected from the group consisting of phosphates, phosphites, phosphonites, phosphines and mixtures thereof, c) 200 ppm to 4500 ppm of one or more branched aliphatic hydrocarbons, wherein squalane is present as branched aliphatic hydrocarbon, d) 100 ppm to 4000 ppm of one or more demolding agents based on a fatty acid ester, e) 0 ppm to 1000 ppm of one or more phenolic antioxidants, f) 0 ppm to 6000 ppm of one or more UV absorbers and g) 0 ppm to 50 000 ppm of one or more further additives, wherein the reported amounts in ppm are in each case based on the total weight of thermoplastic polymer of component a.

2. The LED illumination unit as claimed in claim 1, wherein the number of carbon atoms comprised by the hydrocarbon(s) of component c is 20 to 80 and methyl groups are present as branchings.

3. The LED illumination unit as claimed in claim 2, wherein the weight fraction of methyl groups present as branchings is 10% to 30% by weight based on the carbon atoms in the chain.

4. The LED illumination unit as claimed in claim 1, wherein the hydrocarbon(s) of component c are constructed from coupled farnesane units.

5. The LED illumination unit as claimed in claim 1, wherein at least triphenylphosphine is present as heat stabilizer of component b.

6. The LED illumination unit as claimed in claim 1, wherein at least glycerol monostearate is present as demoulding agent of component d.

7. The LED lighting unit as claimed in claim 1, wherein the composition additionally contains a phenolic antioxidant in an amount of 50 ppm to 1000 ppm.

8. The LED lighting unit as claimed in claim 1, wherein the amount of component b is 200 to 1000 ppm and the amount of component d) is 150 bis 500 ppm.

9. The LED lighting unit as claimed in claim 1, wherein the light emitted by the LED lighting unit has a color temperature determined according to DIN EN 12665:2009 of 2500 K to 7000 K.

10. The LED lighting unit as claimed in claim 1, wherein the thermoplastic composition consists of a) aromatic polycarbonate, b) 10-2500 ppm of one or more phosphorus-based heat stabilizers, selected from the group consisting of phosphates, phosphites, phosphonites, phosphines and mixtures thereof, c) 200 ppm to 4500 ppm of one or more branched aliphatic hydrocarbons, wherein squalane is present as branched aliphatic hydrocarbon, d) 100 ppm to 4000 ppm of one or more demolding agents based on a fatty acid ester, e) 0 to 1000 ppm of one or more phenolic antioxidants, f) 0 ppm to 6000 ppm of one or more UV absorbers, g) 0 ppm to 500 000 ppm of one or more further additives selected from the group consisting of antioxidants distinct from component e, mold release agents distinct from component d, flame retardants, anti-drip agents, stabilizers distinct from component b, optical brighteners, light scattering agents, colorants, wherein the reported amounts in ppm are in each case based on the total weight of thermoplastic aromatic polycarbonate.

11. A method comprising utilizing branched aliphatic hydrocarbons and increasing light transmission in the range from 360 to 460 nm of a thermoplastic composition based on a thermoplastic polymer.

12. The method as claimed in claim 11, wherein aromatic polycarbonate is present in the composition as thermoplastic polymer and squalane is employed as branched aliphatic hydrocarbon.

Description

EXAMPLES

(1) Materials: PC1: Aromatic polycarbonate from Covestro Deutschland AG having an MVR of about 33 cm.sup.3/(10 min) measured at 300° C. and at 1.2 kg load (according to ISO 1133-1:2012-03) which is based on bisphenol A and terminated with tert-butylphenol. Produced in the interfacial process. The polycarbonate contains 250 ppm of triphenylphosphine and 300 ppm of glycerol monostearate (based on the amount of polycarbonate in the total composition of the respective example). Used for examples V1 to V12 and E13 to E16. PC2: Aromatic polycarbonate from Covestro Deutschland AG having an MVR of about 34 cm.sup.3/(10 min) measured at 300° C. and at 1.2 kg load (according to ISO 1133-1:2012-03) which is based on bisphenol A and terminated with tert-butylphenol. The polycarbonate contains 250 ppm of triphenylphosphine and 300 ppm of glycerol monostearate (based on the amount of polycarbonate in the total composition of the respective example). Produced in the interfacial process. Used for comparative examples V17 and V18. PC3: Aromatic polycarbonate from Covestro Deutschland AG having an MVR of about 55 cm.sup.3/(10 min) measured at 300° C. and at 1.2 kg load (according to ISO 1133-1:2012-03) which is based on bisphenol A and terminated with tert-butylphenol. Produced in the interfacial process. The polycarbonate contains 250 ppm of glycerol monostearate (based on the amount of polycarbonate in the total composition of the respective example). A1: Metablen TP-003 from Mitsubishi Chemical Europe GmbH. Flow assistant for polycarbonate based on a phenyl-substituted methacrylate-styrene-acrylonitrile copolymer. A2: Disflamoll® TP from Lanxess Deutschland GmbH. Triphenyl phosphate; CAS No. 115-86-6. A3: Zeonor® 1420R from Zeon Corp., Chiyoda, Japan. Cylcoolefin copolymer (COP). A4: Dianal BR87 from Mitsubishi Rayon. Polymethyl methacrylate having a molecular weight of about 25 000 g/mol, determined using an Ostwald viscometer by measuring intrinsic viscosity in chloroform at 25° C., and a refractive index of 1.490. A5: Squalane from Merck KGaA, Darmstadt, Germany. 2,6,10,15,19,23-hexamethyltetracosane; CAS No. 111-01-3. A6: Dimodan® HAB Veg from DuPont. A glycerol monostearate. A7: Triphenylphosphine from BASF SE; CAS No. 603-35-0.

(2) Procedure:

(3) Experiments for Producing Specimen Sheets for Optical Measurement (40 mm×38 mm×20 mm), V1 to V12, E13-E16

(4) The polycarbonate raw material PC1 was dried in an dry air dryer at 120° C. for 3 hours. 10 kg of the thus-dried material was then filled into a 25 l vessel, the previously weighed-out additive was added and the mixture was mixed in a tumble mixer for 10 min. The mixing step was omitted for V1.

(5) In the subsequent injection molding the mixture was supplied by the material feed hopper of a Krauss Maffei 80-38 injection molding machine and then injection molded in a multilayer process at a melt temperature of 260° C. Optical specimen sheets having dimensions of 40 mm×38 mm×20 mm were injection molded.

(6) Cycle Times:

(7) premold 213 s; postmold 147 s; total cycle time: 360 s.

(8) Experiments for Producing Specimen Sheets for Optical Measurement (40 mm×38 mm×20 mm) V17 and V18:

(9) The polycarbonate raw material PC2 was dried in an dry air dryer at 120° C. for 3 hours. 10 kg of the thus-dried material was then filled into a 25 l vessel, the previously weighed-out additive was added and the mixture was mixed in a tumble mixer for 10 min. The mixing step was omitted for V18.

(10) In the subsequent injection molding the mixture was supplied by the material feed hopper of a Krauss Maffei 80-38 injection molding machine and then injection molded in a multilayer process at a melt temperature of 260° C. Optical specimen sheets having dimensions of 40 mm×38 mm×20 mm were injection molded.

(11) Cycle Times:

(12) premold 213 s; postmold 147 s; total cycle time: 360 s.

(13) Production of Compounds 19V and E20

(14) Compounding carried out in a Berstorff twin-screw extruder at a melt temperature of 275° C. and an extruder speed of 100 rpm.

(15) The PC3 pellet material was dried under vacuum at 110° C. for 3 hours and then compounded with the additives. A powder mixture was used to disperse the additives. To this end the additives were dispersed in a polycarbonate powder (aromatic polycarbonate from Covestro Deutschland AG having an MVR of about 19 cm.sup.3/(10 min) measured at 300° C. and at 1.2 kg load (according to ISO 1133-1:2012-03) which is based on bisphenol A and terminated with tert-butylphenol. This powder is added in an amount of 5% by weight. The additives were added such that the amounts reported hereinbelow resulted.

(16) Additive amounts (based on the amount of polycarbonate in the total composition of the respective example):

(17) V19: 2000 ppm of squalane

(18) E20: 250 ppm of triphenylphosphine (A7) and 2000 ppm of squalane

(19) Production of Test Specimens (60 mm×40 mm×4 mm) for V19, E20

(20) The compounded pellet material was dried under reduced pressure at 120° C. for 3 hours and then processed in an Arburg 370 injection molding machine with an injection unit at a melt temperature of 280° C. and a mold temperature of 80° C. to afford small color specimen sheets having dimensions of 60 mm×40 mm×4 mm (width×height×thickness).

(21) Production of Compounds V21, E22 to E24

(22) Compounding carried out in a Berstorff twin-screw extruder at a melt temperature of 275° C. and an extruder speed of 100 rpm.

(23) The PC1 granulate was dried under vacuum at 110° C. for 3 hours and then compounded with the additives. A powder mixture was used to disperse the additives. To this end the additives were dispersed in a polycarbonate powder (aromatic polycarbonate from Covestro Deutschland AG having an MVR of about 19 cm.sup.3/(10 min) measured at 300° C. and at 1.2 kg load (according to ISO 1133-1:2012-03) which is based on bisphenol A and terminated with tert-butylphenol. This powder is added in an amount of 5% by weight. The additives were added such that the amounts reported hereinbelow resulted.

(24) Additive amounts (based on the amount of polycarbonate in the total composition of the respective example):

(25) V21: --

(26) E22: 1000 ppm of squalane

(27) E23: 2000 ppm of squalane

(28) E24: 3000 ppm of squalane

(29) Determination Methods:

(30) Optical Measurement of Small Color Specimen Sheets of 4 mm Thickness and of Cuboids of 20 mm Thickness:

(31) Optical measurement was carried out using a Perkin Elmer Lambda 950 spectrophotometer with a photometer sphere.

(32) The same methods for determining light transmission, yellowness index and haze were used for the cuboids of 40×38×20 mm and for the small color specimen sheets of 60×40×4 mm,

(33) Transmission measurements—light transmission (Ty, T)—also at 360 to 460 nm were performed on a Lambda 950 spectrophotometer from Perkin Elmer with a photometer sphere according to ISO 13468-2:2006 (i.e. determination of total transmission by measurement of diffuse transmission and direct transmission). Evaluation was carried out by examination in 5 nm steps.

(34) Yellowness index (Y.I.) was determined according to ASTM E 313-15 (observer: 10°/light type: D65) with a Lambda 950 spectrophotometer from Perkin Elmer with a photometer sphere.

(35) Haze was determined according to ASTM D1003:2013.

(36) The glass transition temperature T.sub.g was measured by DSC in a differential scanning calorimeter (Mettler DSC 3+) at a heating rate of 10 K/min (atmosphere: 50 ml/min of nitrogen) in standard crucibles over a temperature range of 0° C.-280° C. The value determined in the 2nd heating operation was reported. Measurement was carried out according to ISO 11357-2:2014-07

(37) TABLE-US-00001 TABLE 1a Processing experiments with PC1 at 260° C., 20 mm cuboids Additive concentration ΔT at ΔT at A1-A6 Ty ΔTy 380 nm 360-460 nm ΔHaze Ex. Additive (% by wt.) (%) (%) (%) (%) ΔYI YI (%) 1V — — 88.87 3.13 2V A1 0.1 88.49 −0.38 −1.93 −26.29 0.26 3.39 −0.02 3V A1 0.2 88.71 −0.16 −0.75 −10.06 0.03 3.16 0.02 4V A1 0.3 88.77 −0.10 −0.90 −10.80 0.05 3.18 −0.11 5V A1 0.4 88.69 −0.18 −2.36 −31.45 0.57 3.70 0.08 6V A2 0.1 88.57 −0.30 −2.49 −28.68 0.15 3.28 −0.06 7V A2 0.2 88.63 −0.24 −2.33 −24.18 −0.06 3.07 −0.05 8V A2 0.3 88.75 −0.12 −1.94 −17.76 −0.18 2.95 −0.20 9V A2 0.4 88.84 −0.03 −1.74 −14.48 −0.18 2.95 −0.40 10V  A3 0.2 78.22 −10.65 −22.03 −406.73  10.39 13.52 56.38 11V  A4 0.1 88.46 0.12* −2.27* −28*   0.49 4.13 −0.04 12V  A4 0.2 88.62 0.28* −3.14* −31*   −0.01 3.63 0.09 13E.sup.  A5 0.1 88.89 0.02 1.84  22.19 −0.09 3.04 −0.39 14E.sup.  A5 0.2 88.91 0.03 2.23  27.57 −0.16 2.97 −0.46 15E.sup.  A5 0.3 88.85 −0.02 2.13  24.95 −0.05 3.08 −0.46 16E.sup.  A5 0.4 88.88 0.00 2.39  28.72 −0.12 3.01 −0.37 *based on the total composition

(38) TABLE-US-00002 TABLE 1b Processing experiments with PC2 at 260° C., 20 mm cuboids Additive concentration ΔT at ΔT at A1-A6 Ty ΔTy 380 nm 360-460 nm ΔHaze Ex. Additive (% by wt.) (%) (%) (%) (%) ΔYI YI (%) 18V — — 88.34 3.64 17V A6 0.08 87.48* −0.86* −7.47* −98 1.02 4.67 0.31 *based on the total composition

(39) TABLE-US-00003 TABLE 2 Processing experiments with PC2 at 260° C., 4 mm small color specimen sheets ΔT at ΔT at Ty ΔTy 380 nm 360-460 nm ΔHaze Ex. (%) (%) (%) (%) ΔYI YI (%) 19V 89.51 2.10 E20 89.77 0.26 6.67 40.7 −0.97 1.13 −0.07

(40) The Δ values are in each case based on the corresponding value of the reference example 1V; at 10V, 11V and 17V, the Δ values are in each case based on the corresponding value of the reference example 18V.

(41) TABLE-US-00004 TABLE 3 T.sub.g values Ex. T.sub.g [° C.] V21 145.2 E22 145.0 E23 144.0 E24 143.3

(42) The examples show that in most cases addition of the additives markedly reduces the total transmission Ty (ΔTy negative). Only addition of PMMA (A4), as also described in DE 60116498 T2, causes transmission to be slightly increased. However, transmission in the range from 360-460 nm is reduced. This is disadvantageous especially for LED applications since the LEDs normally used in the described applications provide the most energy precisely in this spectral range. A greater absorption in this range results in poorer long-term performance.

(43) Additive A1 is known as a flow auxiliary. Improved flowability in principle makes it possible to reduce damage during thermal processing in extruders or injection molding machines since reduced shear forces are applied. It was therefore surprising that no improvement in terms of transmission and yellowness index was achievable using this additive.

(44) Low molecular weight additives such as A3 can likewise increase flowability but without having a positive effect on the optical properties in the relevant transmission range.

(45) Like additive A6, additive A5 has a demolding effect. However, a further addition of A6 as demolding agent has no significant effect or leads to significantly reduced transmission at 380 nm while, surprisingly, the use of A5 even in small amounts leads to an improvement in the optical properties, especially in the relevant transmission range.

(46) Only in the inventive examples do the total transmission Ty and the transmission in the range from 360 nm to 460 nm increase while, at the same time, yellowness index and haze are also reduced compared to reference example 1V, i.e. a corresponding polycarbonate composition without squalane.