WO2021110869A1

WO2021110869A1 - Polyurethane casting resin having high uv transparency and high temperature stability

Info

Publication number: WO2021110869A1
Application number: PCT/EP2020/084530
Authority: WO
Inventors: Martin Burkhardt; Alexander KALTENBACH; Dirk Krüger; Joachim Bauer; Marko Gutke; Sigurd Schrader
Original assignee: Technische Hochschule Wildau; resintec GmbH
Priority date: 2019-12-04
Filing date: 2020-12-03
Publication date: 2021-06-10
Also published as: DE102019133078A1; DE112020005915A5

Abstract

The invention relates to a polyurethane which is characterized by very good optical transparency, thermal stability, high surface tension and a very long pot life and thus by advantageous processability, and which is suitable in particular for the production of optical assemblies such as lenses (1) and a lamp unit having a lens produced in said manner. The polyurethane consists of two components, a resin component made of polyester-polyol and a hardener component consisting of a hexamethylene diiosocyanate oligomer, the composition of which has been optimized for optical applications and fulfills the specific requirements of production for optical assemblies specifically for the potting of micro LEDs. The present invention is characterized in that the refractive index of the material is approximately 1.5, the Abbe number is approximately 40 and the transparency at a thickness of 1 mm is approximately 91% from a wavelength of 300 nm. The polymer has a bandgap or lumo-homo gap of Eg ≈ 5 eV and thus has exceptional transparency in the UV and VIS range and is ideally suited for producing optical lenses and potting material having lens molding for high-performance LEDs. The material also fulfills all thermal and mechanical requirements for potting materials and lenses for LEDs.

Description

Polyurethane casting resin with high UV transparency and high temperature stability

The invention relates to a highly transparent and thermally stable polyurethane casting resin which can be used for the production of lenses and lenses for lighting units in conjunction with light sources or light guides. It is important that the material meets the specific requirements for encapsulating micro-LEDs with simultaneous high transmission in the ultraviolet and visible spectral range (UV / VIS range).

The current requirements and the market volume for light-emitting diodes (LEDs) and miniaturized CMOS image sensors have led to an increasing demand for inexpensive optics and a significant expansion of production capacities. LEDs are considered to be highly efficient light sources that offer a long service life, a wide range of colors and design options.

The present invention is based on the object of developing a polymer which protects the LED chips from environmental influences, the applied polymer also being used to shape the beam of the emitted light. The optical properties of the polymers used are therefore of great importance for the light yield and the beam shaping properties. It is therefore of great importance to develop an optical high-performance plastic that combines and unites excellent UV and VIS transparency with high thermal stability, good hardness, high surface tension and a relatively long pot life.

The polyurethane casting resin according to the invention is a two-component polyurethane casting resin, the first component being a resin, in particular a polyol, and the second component being a hardener made from an isocyanate.

In one embodiment, the material preferably consists of a polyester polyol and a hexamethylene diisocyanate oligomer (HMDI). The casting resin preferably consists of> 40% by weight polyester-polyol and> 15% by weight isocyanate. The polyols contain reactive hydroxyl (OH) groups which react with isocyanate (NCO) groups on isocyanates to form polyurethanes. The number of hydroxyl (OH) groups depends on the starting materials of the polyol synthesis. According to “M. lonecu, Chemistry and Technology of Polyols for Polyurethanes, Rapra Technology Limited, ISBN: 1-85957-491-2, 2005 ”for example glycerol, pentaerythritol, xylithol and sorbitol with an aliphatic structure and trimethylolpropane, triethanolamine, dipentaerythriol, a-methylglucoside and Sucrose with a cycloaliphatic structure is known and suitable according to the invention. These materials advantageously have an f with 3-8 reactive OH groups (“f”: OH functionality per molecule). Other suitable starters are aliphatic or aromatic polyamines with 2-3 amino groups (-NH ₂ ) / mol, such as ethylenediamine (EDA) f = 4, diethylenetriamine (DETA) f = 5, ortho-toluenediamine (o-TDA) f = 4 and diphenylmethane diamine (MDA) f = 4. A third group of starters are Nowola (c) ke with a high number of OH groups or Mannich base-based aromatic compounds (f = 3-5). The starters of the synthesis react with alkylene oxide (for example propylene oxide or ethylene oxide) to form the polyester polyols or polyester resin according to the invention.

From EP 2 910 586 A1 it is known that for transparent polyurethane with a high glass transition temperature T _g the polyisocyanate component consists of one or more polyisocyanates and the polyisocyanate component has an average NCO functionality per molecule of> 3 and the polyol component consists of one or more polyols and the polyol component has an average OH functionality per molecule of> 3 and an OH content of> 25% by weight. having.

It is therefore a further object of the present invention to produce an optimized polyurethane that, due to its properties, has excellent transparency, temperature stability, good mechanical properties and stability, so that it is particularly suitable and used for use as a lens, LED or other optical components can be. This problem is solved by at least one patent claim.

The polyurethane casting resin optimized according to the invention is preferably composed of two components, namely a resin component and a hardener component for the production of the polyurethane, such an organic compound with a functional urethane group -NH-CO-O-, the resin component being a Polyester-polyol (polyester resin) with an average OH functionality per molecule of 2-3 and an OH content of at least 130 mg KOH / g, determined according to DIN 53240-2: 207-11. The method mentioned in DIN 53240-2 is based on a catalyzed acetylation of the hydroxyl group. After hydrolysis of the intermediate product, the remaining acetic acid is titrated in a non-aqueous medium with an alcoholic KOH solution and the OH content can be given in mg KOH / g. It is also preferred that the polyester-polyol has a weight average M _w of 800-1350 g / mol.

The hardener component is preferably a hexamethylene diisocyanate oligomer with an average NCO functionality per molecule of approx. 2, in particular 2-3 and an NCO content of> 15% by weight, in particular> 20% by weight. Hexamethylene diisocyanate oligomer. Hexamethylene diisocyanate oligomers are available from 1,6-hexamethylene diisocyanate (HMDI) monomers, which, for example, give 1- (6- isocyanatohexyl) -3,5-bis (5-isocyanatopentyl) -1, 3,5-triazinane-2,4, 6-trione or higher isocyanurates can oligomerize. It is preferred that 2 to 10 1, 6-

Hexamethylene diisocyanate (HMDI) oligomerize monomers to form a hexamethylene diisocyanate oligomer. This leads to an advantageous networking. Such hexamethylene diisocyanate oligomers are also commercially available (e.g. Spies Hecker, Cologne, Germany).

The problem of UV transmission of the many optical plastics with the polyurethane casting resin optimized according to the invention has thus been advantageously solved and new potentials arise for the use of the material optimized according to the invention with a band gap or Lumo-Homo Gap (Eg) of ^« 4, 9-5, 0-5.1 eV

(Wavelength A-250 nm). At a wavelength l> 300 nm and a thickness of 1 mm, the material shows transmissions of outstanding ^ 90%. The refractive indices are, n _F (l = 486.1 nm) = 1.492, n _D (l = 589.3 _{nm) = 1.481 and n c} (l = 656.3 nm) = 1.477 and the material has an Abbe -Number of 40. These properties are comparable and exceed the performance of other optical plastics, for example in the statements by "William S. Beich, Nicholas Turnera GS Plastic Optics, 408 St. Paul Street, Rochester, NY 14605, Polymer Optics Design , Fabrication, and Materials, edited by David H. Krevor, William S. Beich, Proc. of SPIE Vol. 7788, 778805 and are compared in Table 1.

In a preferred embodiment, the invention therefore relates to a polyurethane according to the invention, the refractive indices determined from transmission and reflection measurements being approximately 1.5 and the Abbe number assuming a value of 38 to 42.

The polyurethane casting resin optimized according to the invention shows excellent transmission in the UV range, which is documented in Table 1 at the wavelength of 300 nm.

The transmission was determined from reflection and transmission measurements on thin layers and on thick flat plates of 8 mm. The 50% transmission losses are caused by reflection and absorption. The slight light scattering is integrated by measuring the transmission using an integrating sphere.

Therefore, in a preferred embodiment, the invention relates to a polyurethane according to the invention, where with a layer thickness of approx. 5 mm only about 50% of the incident radiation with a wavelength of up to 300 nm is transmitted.

The invention also relates to a polyurethane according to the invention, the radiation in the wavelength range from 380 to 780 nm not being absorbed, i.e. advantageously being selected.

In addition, the invention relates to a polyurethane according to the invention, where with a layer thickness of approx. 5 mm 0.5 to 1% of the incident visible radiation is scattered.

With thin layers <10 pm, transmissions of 90% up to a wavelength l = 250 nm are possible.

The polyurethane according to the invention has the special properties of a low viscosity of approx. 2000 mPa * s and a long pot life of> 24 h. The polyurethane casting resin optimized according to the invention has an initial mixed density (p [g / ml_]) of 1.14 at 23 ° C. and an initial mixed viscosity (h [mPa * s]) of 2000. It has a pot life (Tz [min]) of approx 1440 (approx. 24 hours) at 23 ° C and hardens in 2 hours at 120 ° C.

In a preferred embodiment, the invention therefore relates to a polyurethane according to the invention which has a viscosity of 2000 to 2800 mPa * s, in particular up to 3200 mPa * s and / or is so viscous that it can be processed using a dispensing method.

The viscosity and the long pot life enable time and cost-saving manufacturing techniques based on dispensing systems, the designs of which are available from “K. Angermaier, PH. Müller, save time and money, UV-curing silicones, Carl Hanser Verlag, Munich, Kunststoffe 4/2010 ", in the patent application with the file number EP19196944 (filed on September 12, 2019)," WM Lee, A. Upadhya, PJ Reece. Tri Giang Phan, Fabricating low cost and high performance elastomer lenses using hanging droplets, Biomedical Optics Express 5, 1626 (2014) "and" Chien-Lin Chang Chien, Yu-Che Huang, Syue-FongHu, Chung-Min Chang, Ming- Chuen Yip, Weileun Fang, Polymer dispensing and embossing technology for the lens type LED packaging, J. Micromech. Microeng. 23 (2013) 065019 “and are suitable for use in mass production. In addition, the polyurethane optimized according to the invention enables casting resin due to its relatively high Surface tension of> 45 dyn / cm in combination with the application as a potting compound also an additional formation of lenses, for example to control the beam angle of LEDs. The polyurethane casting resin optimized according to the invention is also of potential interest for the production of polymer lenses and polymer lens arrays, as shown in the above-mentioned patent application with the file number EP 19196944. These polymer lenses and polymer lens arrays can be used in the optical industry for lighting optics (eg street lighting) for desired light distributions, whereby specific color properties can also be included in the lighting system optimization.

The flow properties and the surface tension of the material ensure that the material, in connection with the particularly advantageous way of direct application to semiconductor substrates or light guides, is also used for encapsulating light sources, in particular LEDs arranged on semiconductor substrates and for packaging LEDs with lens shaping (e.g. Chip-on-Board (CoB) LEDs) is suitable. The high surface tension of the material of> 45 dynes / cm, with a non-polar proportion of 92%, and the curing behavior allow different geometrical lenses to be manufactured with flexible selection of the mixing ratio for different forms of application. In this case, high hardnesses of Shore A> 80, in particular a Shore A hardness of 82 to 90, are achieved after curing, and high scratch resistance is achieved.

The polyurethane cast resin resin optimized according to the invention has a temperature resistance in continuous use of at least 120 ° C, shows high temporary temperature stability of 300-400 ° C and a temperature stability in soldering processes at 260 ° C and is used to protect the LEDs from external influences (moisture, Vibrations, dust, UV etc.) and shows a decomposition temperature of> 350 ° C by means of dynamic differential calorimetry (DSC) and thermogravimetric analysis (TGA).

In a preferred embodiment, the invention therefore relates to a polyurethane according to the invention which has a glass transition temperature of -12 to -13 ° C, in particular -12.5 ° C and a decomposition temperature of at least 350 ° C.

Table 1: Comparison of the optical properties of the casting resin optimized according to the invention with other optical synthetic resins, published in “William S. Beich, Nicholas Turnera GS Plastic Optics, 408 St. Paul Street, Rochester, NY 14605, Polymer Optics Design, Fabrication, and Materials, edited by David H. Krevor, William S. Beich, Proc. of SPIE Vol. 7788, 778805 ". The thickness of all materials is 3,741 mm.

^* Abbe number V _d = (n _d - 1) / (n _F - nc), n _d = 587.6 nm

** The refractive indices were determined by reflection and transmission measurements, which were measured with the LAMBDA 1050 UV / Vis / NIR spectrometer from Perkin Elmer.

*** The transmission for 3741 mm was calculated using the optical constants from the measurements of the reflection and transmission on samples of different thicknesses.

The invention also relates to the use of a polyurethane according to the invention for the production of optical assemblies, lenses, packaging of LEDs with lens shaping, light guides, optical fiber coating with lens formation, sensors with lenses, chip-integrated LEDs, light units for light sources and microlens arrays or a corresponding method, the polyurethane according to the invention is used for manufacturing purposes. The invention also relates to the use of an inventive

Polyurethane for coating at least one electrically conductive component, an electronic component, an optical assembly, lenses, packaging of LEDs with lens shaping, light guide, optical fiber coating with lens formation,

Sensors with lenses, chip-integrated LEDs, light units for light sources and / or microlens arrays or a corresponding method, the polyurethane according to the invention being used for production purposes.

The invention also relates to the use of a polyurethane according to the invention, at least one lens being produced using the polyurethane by means of a dispensing and / or dropping process, or a corresponding process, the polyurethane according to the invention being used for production purposes.

In the following, the invention will be explained in more detail without restricting the general inventive concept on the basis of an exemplary embodiment with reference to the figure. It shows:

1: Forming of a polymer lens using a polyurethane casting resin optimized according to the invention for a CoB-LED with housing and the associated measurement result of the light distribution along the main axes of the CoB-LED at a wavelength of 525 nm.

According to the embodiment shown in Fig. 1, the two components (polyester-polyol and hexamethylene diisocyanate oligomer) were mixed in a mixing ratio of 100: 60% by weight, and heated to 50 ° C with the magnetic stirrer IKA C-Mag HS7 homogenized for 2 min. The Eppendorf EDOS-5221 dispenser was used to manufacture microlenses. The polyurethane was cured in an oven at 120 ° C. for 2 hours. Figures 1a) and 1b) show an InGaN CoB-LED 1 with the Cpip dimensions of 250x250 pm in a ceramic housing 2 from EPIGAP Optronic GmbH with the dimensions 2x2, 5x1 mm (width, height, depth) with a microlens 3, which was coated with the aid of the highly transparent and temperature-stable material 4 according to the invention by dispensing, the special lens shape being produced by drop dispensing and subsequent drying or hardening. Before the dispense coating, the housing surface was modified with polytetrafluoroethylene (PTFE) in order to reduce the radius of the microlens even further. In addition, FIG. 1 c) shows the associated measurement result of the targeted light distribution at a wavelength of 525 nm.

Claims

1. Polyurethane made from at least one resin component and at least one hardener component, the at least one resin component being a polyester-polyol with an average OH functionality per molecule of about 2 or 2-3 and an OH content of at least 130 mg KOH / g, and the at least one hardener component is a hexamethylene diisocyanate oligomer with an average NCO functionality per molecule of about 2 or 2-3 and an NCO content of at least 15% by weight.

2. Polyurethane according to claim 1, characterized in that the radiation in the wavelength range from 380 to 780 nm is not absorbed.

3. Polyurethane according to claim 1 or 2, characterized in that with a layer thickness of approx. 5 mm, only about 50% of the incident radiation with a wavelength of up to 300 nm is transmitted.

4. Polyurethane according to one of the preceding claims, characterized in that with a layer thickness of approx. 5 mm, 0.5 to 1% of the incident visible radiation is scattered.

5. Polyurethane according to one of the preceding claims, characterized in that the band gap or Lumo-Homo Gap (Eg) determined from transmission and reflection measurements is «4.9-5.0-5.1 eV and therefore in the pm range for thin layers is transparent up to 250 nm.

6. Polyurethane according to one of the preceding claims, characterized in that the refractive indices determined from transmission and reflection measurements are approximately 1.5 and the Abbe number assumes a value of 38 to 42.

7. Polyurethane according to one of the preceding claims, characterized in that it has a viscosity of 2000 to 2800 mPa * s, in particular up to 3200 mPa * s and / or is so viscous that it can be processed with a dispensing method.

8. Polyurethane according to one of the preceding claims, characterized in that there is a pot life of at least 24 h at least at 23 C owns.

9. Polyurethane according to one of the preceding claims, characterized in that the polyurethane has a glass transition temperature of -12 to -13 ° C, in particular of -12.5 ° C and a decomposition temperature, measured by means of dynamic differential calorimetry (DSC) and thermogravimetric analysis (TGA) of at least 350 ° C.

10. Polyurethane according to one of the preceding claims, characterized in that it has a Shore A hardness of 82 to 90.

11. Polyurethane according to one of the preceding claims, characterized in that it has a surface tension of at least 45 dynes / cm, with a non-polar proportion of at least 90%.

12. Use of a polyurethane according to one of claims 1-11 for the production of optical assemblies, lenses, packaging of LEDs with lens shaping, light guides, optical fiber coating with lens formation, sensors with lenses, chip-integrated LEDs, light units for light sources and microlens arrays.

13. Use of a polyurethane according to one of claims 1-11 for coating at least one electrically conductive component, an electronic component, an optical assembly, lenses, packaging of LEDs with lens shaping, light guides, optical fiber coating with lens formation, sensors with lenses, chip-integrated LEDs, lighting units for light sources and / or microlens arrays.

14. Use of a polyurethane according to any one of claims 1-11, characterized in that at least one lens is produced using the polyurethane by means of a dispensing and / or dropping process.

15. A method for producing a polyurethane according to any one of claims 1 to

12, in which at least one resin component is a polyester polyol with an average OH functionality per molecule of about 2 or 2-3 and an OH content of at least 130 mg KOH / g and at least one hardener component is a hexamethylene diisocyanate oligomer with an average NCO -Functionality per molecule of about 2 or 2-3 and an NCO content of at least 15% by weight, in particular in a ratio of (resin component: hardener component) 100: 40% by weight to 100: 60% by weight.