Abstract:
A method is provided for production of a module, including the steps of: (a) providing a substrate ( 1 ) having a first surface ( 5 ); (b) providing an open casting mold ( 6 ), wherein the formation of at least one optical element ( 4, 4′ ) is provided in the casting mold ( 6 ); (c) coating the first surface ( 5 ) with an adhesion promoter ( 2 ); (d) covering the coated surface ( 2, 5 ) with a silicone ( 3 ) in the open casting mold while forming the optical element from the silicone ( 3 ); and (e) curing the silicone in the casting mold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Section 371 of International Application No. PCT/EP2013/000860, filed Mar. 21, 2013, which was published in the German language on Nov. 7, 2013, under International Publication No. WO 2013/164052 A1 and the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a method for producing an optical module comprising covering a first surface of a substrate with a silicone in an open casting mold. The invention also relates to an optical module comprising a substrate having a first surface and a layer of silicone applied onto the first surface, whereby an optical element is provided in the layer of silicone. 
         [0003]    International Publication No. WO 2012/031703 A1 describes a production method for chip-on-board modules, in which a substrate comprises a plate-shaped carrier having multiple LEDs, wherein a surface of the substrate is provided, in an open casting mold, with a cover made up of a layer for providing an optical system. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    It is an object of the invention to provide a method for producing an optical module that allows for a high degree of flexibility in the selection of a silicone used in it. 
         [0005]    The object is met by a method for producing an optical module, comprising the steps of: 
         [0006]    a. Providing a substrate having a first surface; 
         [0007]    b. Providing an open casting mold, wherein the formation of at least one optical element is provided in the casting mold; 
         [0008]    c. Coating the first surface with an adhesion promoter; 
         [0009]    d. Covering the coated surface with a silicone in the open casting mold while forming the optical element from the silicone; and 
         [0010]    e. Curing the silicone in the casting mold. 
         [0011]    Applying an adhesion promoter onto the surface of the substrate to be coated allows the admixture of additives to the silicone in the casting mold to be avoided or reduced. Moreover, a broader range of silicones is available for coating. Another advantageous effect is the good release of the cured silicone from the casting mold. In particular, the casting mold does not need to be coated or lined with release film by this means in the present case. 
         [0012]    In the scope of the invention, an optical element shall be understood to mean any formation in the layer that permits for well-defined transmission of light, including in the UV range and/or IR range depending on the requirements. Preferred embodiments can have the optical element be a lens, for example a collecting lens, dispersing lens, cylinder lens, Fresnel lens, or the like. In other embodiments, the optical element can just as well consist of light scattering, diffraction by a prism or the like. The formation of plane-parallel surfaces for simple transmission of light is an optical system according to the scope of the invention. The polymeric layer having the optical element formed therein forms an optical system that is arranged right on the substrate. 
         [0013]    The substrate in the casting mold can be covered in a variety of ways. Either the silicone can be added to the casting mold first, followed by the substrate being immersed into the silicone. Alternatively, the substrate can first be inserted into the at least partly empty casting mold, followed by adding the silicone in controlled manner. In either case, the casting mold contains preferred structures, such as fins, lugs or the like, on which the substrate is supported and positioned. 
         [0014]    In a preferred exemplary embodiment, the silicone contains no admixture of adhesion promoter. This allows especially good UV translucence, among other factors, to be attained. 
         [0015]    Preferably, the silicone can contain a catalyst for initiation of a curing process. This may concern, for example, very small admixtures of platinum or similar substances. The catalytically-induced curing allows high purity of the silicone to be attained. It is particularly preferred for the silicone not to be cured by UV light, since high translucence for UV light is especially desired in many cases. 
         [0016]    Moreover, the method preferably comprises the step of heating the silicone in the casting mold to a defined temperature in order to initiate and/or accelerate a curing process. Catalytically-induced curing, for example, can be accelerated by heating which renders the method more effective and reduces the amount of catalyst required even further. However, curing processes that proceed just by elevated temperature are conceivable just as well. Typical defined temperatures are below ranges in which embrittlement or other degeneration of the silicone is to be expected. Exemplary temperature ranges are at approx. 100° C., preferably less than 140° C. The defined temperature depends on which temperatures are compatible with the substrate, among other factors. 
         [0017]    A particularly preferred embodiment provides the silicone as a mixture of at least two silicones right before placing it in the casting mold. Such two- or multi-component systems are commercially available, wherein mixing two, in particular, highly pure silicones in turn produces highly pure silicone again with the mixing initiating a curing process and/or a cross-linking process. Accordingly, one of the silicones can be designed, for example, such that it contains a catalyst for curing the mixture that by itself cannot cross-link the silicone. 
         [0018]    It is generally advantageous for the silicone to be highly pure and to contain less than 100 ppm of foreign substances. It is particularly preferred for the foreign substance content to be less than 10 ppm. The term “foreign substances” shall be understood to mean all organic or other admixtures, except for the catalyst, that are not part of the cross-linked, cured silicone system itself. Admixed adhesion promoters are an example of undesired foreign substances. In general, components comprising carbon chain bonds are also considered to be undesired foreign substances. Bonds of this type are usually not UV-resistant. A silicone that is desired according to the invention therefore comprises, at least after curing, no more than single carbon atoms, for example in the form of methyl residue groups. The high purity of the silicone allows, in particular, especially high UV resistance to be attained. This applies not only to the mechanical resistance of the silicone, but also to an optical durability, since even the presence of minor impurities is associated with premature yellowing of the UV-exposed silicone. 
         [0019]    In order to minimize adverse effects at the transition from substrate to silicone, it is preferred to provide the adhesion promoter to be applied onto the surface with the applied layer having a mean thickness of less than 100 nm. In this context, it is desirable for the optical properties that the thickness of the layer of adhesion promoter be less than half the wavelength of the light passing through the optical element. More preferably, the thickness of the layer is less than 10 nm, in particular no more than 10 monolayers. Due to the function of the adhesion promoter, the application of just a monolayer is ideal and desired. 
         [0020]    The adhesion promoter can be applied to the substrate in a suitable manner, for example by immersion, vapor deposition, application of droplets, spraying, or by spin coating. It is particularly preferred to thin the applied layer after application, for example by blowing off excessive amounts of adhesion promoter. 
         [0021]    Preferably, the adhesion promoter itself is UV-resistant. Degeneration of the adhesion promoter by UV radiation can be tolerated at least if the layer is sufficiently thin. Adhesion promoters for silicones are generally known and depend on the substrate to be used. Adhesion promoters are often molecules possessing a first terminal group that binds to the substrate and a second terminal group that binds to the silicone. The adhesion promoter preferably is an adhesion promoter that binds to the silicone by chemical bonds. The adhesion promoter may bind to the substrate by chemical and/or physical bonds, for example by adhesion or Van-der-Waals forces, depending on the existing circumstances. Typical adhesion promoters consist of a mixture of reactive siloxanes and silicon resins. In particular, the terminal groups can be optimized to suit the substrate. 
         [0022]    For optimization of the open casting method, the invention provides the viscosity of the silicone before curing to be less than 1,000 mPa.s. Preferably, the viscosity is less than 100 mPa.s, particularly preferably less than 50 mPa.s. The above-mentioned low viscosities allow the casting mold to be filled rapidly and without producing bubbles, and allow, in particular, the substrate to be covered without producing bubbles. In this context, any excess of silicone displaced through the substrate being immersed, can flow off easily at an overflow. 
         [0023]    It is generally advantageous for the invention to provide the cured silicone to possess a hardness in the range of 10 to 90 Shore A. It is particularly preferred for the hardness to be in the range of 50 to 75 Shore A. This provides for sufficient mechanical stability to ensure exact shaping even of a sophisticated optical system. Moreover, the high elasticity of the coating provides very good protection from mechanical impacts such as shocks, vibrations or thermally-induced mechanical tension. 
         [0024]    A generally preferred embodiment provides the optical element consisting of silicone to possess long-lasting UV resistance for irradiation intensities in excess of 1 W/cm 2  in the wavelength range below 400 nm. It is particularly preferred for the resistance to also be evident with respect to irradiation intensities in excess of 10 W/cm 2 . It has been evident that highly pure silicone, in particular, is a very good material for use with UV radiation. In this context, long-lasting resistance shall be understood to mean that the radiation exposure can be for a long period of time of at least several months without marked degeneration or color-change and/or yellowing of the silicone. The preferred UV resistance of a module according to the invention is therefore significantly higher than the common UV resistance of materials with respect to sunlight of an estimated approx. 0.15 W/cm 2 . 
         [0025]    In a preferred embodiment of the invention, the substrate comprises a carrier having at least one LED. It is particularly preferred in this context for the optical element to be arranged right on the LED. General reference to modules of this type is made in WO 2012/031703. The substrate can be, in particular, a chip-on-board (COB) module having multiple LEDs and possibly further electronic components. The LEDs can emit light, in particular in the UV range. The peak wavelength of the LEDs that are preferably, but not necessarily, used is in the range from 350 to 450 nm. Preferred sub-ranges are 365±5 nm, 375±5 nm, 385±5 nm, 395±5 nm, and 405±5 nm. Typically, the spectral half-width of an LED is in the range of 20 to 30 nm. The spectral width at the base can be 50 to 70 or more nm. Overall, the method according to the invention allows an LED module to be provided that has a primary optical system of LEDs made of the same material applied to it as a single part. In this context, the LED module particularly preferably emits light in the UV range. 
         [0026]    LED modules of this type can generate high radiation intensity, in particular in the UV range. They can preferably be used for producing lamps that focus high irradiation densities into a defined structure. A particularly preferred use is the production of a device for drying coatings. Devices of this type can be used for the drying of lacquers in printing procedures, in particular in offset printing procedures. 
         [0027]    Another exemplary embodiment provides the substrate to comprise a translucent carrier, wherein the carrier and the optical element jointly form an optical system. In an optical system of this type, the carrier can, in principle, consist of the same or of a different material as or than the layer applied to it. The carrier preferably consists of a glass, for example. This can be, in particular, UV-translucent glass, for example quartz glass. 
         [0028]    Another preferred embodiment provides, in addition, a second surface to be coated after step e, wherein the coating of the second surface also comprises procedural steps a to e. Accordingly, for example, an optical system, having two sides of layers formed to be the same or different, can be produced on a central carrier, for example a glass plate. It is also conceivable to coat a module with LEDs on two sides by this means. In the process, LEDs can be present either on both sides or coating of the second side only serves for protection of the module, e.g. from shocks, ingress of water or the like. 
         [0029]    In this context, the second surface can either be a second surface of the substrate, for example in the case of coating a side of the substrate that is opposite to the first coating, or any other surface. In particular, this can concern an external surface of the first coating onto which a second coating is applied by repeating the application of the method according to the invention. Depending on the existing requirements, the second layer can be applied right onto the first layer. Alternatively, the second surface can just as well belong to an intermediate layer, such as a coat, deposited metal, etc., that is first applied, for example, to the first coating. 
         [0030]    The object of the invention is also met by an optical module, comprising a substrate having a first surface and a layer of silicone applied onto the first surface, wherein an optical element is provided in the layer of silicone by an open casting method, wherein a layer of adhesion promoter is arranged between the first surface and the layer of silicone. Providing the layer of adhesion promoter allows for good connection of the entire surface of the silicone to the substrate. 
         [0031]    Preferably, an optical module according to the invention also comprises one or more features according to the method described and claimed herein. The optical module can be produced, in particular, according to a method according to the invention. But, in principle, the optical module can just as well be produced by a different method. 
         [0032]    The object of the invention is also met by a lamp comprising an optical module according to the invention. 
         [0033]    According to the invention, a lamp of this type is preferably used for drying a layer. This can preferably concern the use in a printing procedure. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0034]    The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
           [0035]      FIG. 1  is a schematic sectional view through a first exemplary embodiment of a module according to the invention. 
           [0036]      FIG. 2  is two schematic sectional views of an open casting mold and a substrate during the production of an optical module according to an embodiment of the invention. 
           [0037]      FIG. 3  is a schematic sectional view of a variant of the casting mold of  FIG. 2 . 
           [0038]      FIG. 4  is schematic sectional views of three variants of an optical module of a second embodiment of the invention. 
           [0039]      FIG. 5  is a schematic sectional view of a first refinement of a module according to  FIG. 4 . 
           [0040]      FIG. 6  is a schematic sectional view of a second refinement of a module according to  FIG. 4 . 
           [0041]      FIG. 7  is a schematic sectional view of an example of a use of a module according to  FIG. 4 . 
           [0042]      FIG. 8  is a schematic sectional view of an example of a combined use of various exemplary embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    An optical module according to  FIG. 1  comprises a substrate  1  onto which a layer of an adhesion promoter  2  has been applied. A shaped layer  3  of silicone has been applied onto the adhesion promoter  2  and comprises, in the present case, a plurality of optical elements  4  in the form of collecting lenses. 
         [0044]    The substrate  1  in the present case consists of a chip-on-board (COB) module having a carrier  1   a  on which multiple LEDs  1   b  are arranged. The adhesion promoter  2  covers a first surface  5  of the substrate that consists in part of a surface of the carrier  1   a  and in part of surfaces of the LEDs  1   b  and of further components (not shown). 
         [0045]    In other exemplary embodiments of the invention according to  FIG. 4  to  FIG. 6 , the substrate does not consist of an LED module, but of a translucent carrier  1 , namely a glass plate in the present case. The carrier  1  and one or more silicone layers  3 ,  3 ′, which have been applied analogously to the first example and have optical elements  4 ,  4 ′ provided therein, jointly form an optical system  10 . In the present case, the substrates and/or translucent carriers  1  each are shown as plates having plane-parallel surfaces. Depending on the existing requirements, the carrier can just as well comprise optical elements, such as lenses, for example. 
         [0046]    In the example on the top according to  FIG. 4 , the optical elements  4  are provided as collecting lenses analogous to the first exemplary embodiment. 
         [0047]    In the example in the middle according to  FIG. 4 , the optical elements  4  are provided as Fresnel lenses. 
         [0048]    In the example on the bottom according to  FIG. 4 , the optical element  4  is provided as a quasi-random collection of light-diffracting structures and/or formations by which a scattering effect is attained. 
         [0049]    The layers  3 ,  3 ′ each consist of a highly pure silicone having a hardness of approx. 65 Shore A. The silicone is colorless and transparent. The silicone is highly translucent in the wavelength range from approx. 300 nm to approx. 1,000 nm. The silicone is UV-resistant to long-lasting irradiation having wavelengths below 400 nm and an energy density in excess of 10 Watt/cm 2 . 
         [0050]    Each of the optical modules described above is produced according to the following method: 
         [0051]    First, an open casting mold  6  (see  FIG. 2 ) is provided that contains the negative molds of the formations for the optical elements  4 . Moreover, supports  6   a  in the form of fins or lugs supporting the substrate  1  in a certain position are provided in the mold  6 . 
         [0052]    Then, the surface  5  of the substrate  1  to be coated is coated with an adhesion promoter  2 , possibly after a cleaning step. The coating then proceeds, for example, by applying droplets of the substance and blowing-off any excess of the substance, which also dries the remaining adhesion promoter. In the ideal case, the thickness of the adhesion promoter applied is equal to just one monolayer, in any case it is preferred to be less than 100 nm. 
         [0053]    As soon as the substrate is prepared as described, a silicone mixture of two components is produced and placed in the open casting mold. One of the components contains a catalyst and the other component contains a cross-linker. The mixture has a viscosity of less than 50 mPa.s in the present case. As a matter of principle, mixing the components initiates the curing process, though this process proceeds quite slowly at low temperatures, such as room temperature. 
         [0054]    Subsequently, the substrate is placed in the casting mold in controlled manner with the coated surface  5  facing downward and immersed into the silicone mixture (see left side of  FIG. 2 ). 
         [0055]    In particular, an overflow  7  can be provided on the casting mold in this context, as shown schematically in  FIG. 3 . The overflow and the low viscosity of the silicone jointly ensure that the depth of immersion of the substrate is well-defined and, in particular, that any silicone displaced by the substrate can flow off. By this means, it can be ensured, if necessary, that not only the surface  5  of the substrate, but also the front sides of the substrate get covered by a circumferential rim  8  of layer  3 , whereas a back side  9  of the substrate is not being coated. Complete enveloping of the substrate may be desirable in other embodiments, though. 
         [0056]    The rim  8  has not only a protective function for the carrier substrate  1 , if this is supported on its rim or upon a number of the modules being arranged edge to edge, but it also enables direct, gap-less, transparent arrangement of the substrates and thus minimization of the deviation of light at the optical boundaries between two carrier substrates. 
         [0057]    Once the substrate is positioned on the supports  6   a,  it is checked according to need whether the surface  5  is wetted completely and, in particular, without forming bubbles. In a possible refinement of the invention, the immersion of the substrate can just as well proceed in a vacuum in order to prevent the air bubble issue. However, due to the viscosity being low, bubble-free coating can generally be attained in the absence of a vacuum as well. 
         [0058]    After positioning, the silicone is cured and/or cross-linked. This is accelerated significantly in expedient manner by increasing the temperature. Typically, curing can be completed in half an hour at a temperature of approx. 100° C. At temperatures in the range of 150° C., curing can typically be completed in just a few minutes. The selection of the temperature for this thermal curing process must also take into consideration the properties of the respective substrate. 
         [0059]    Once the silicone is cured, the substrate, now coated, can be taken out of the re-usable casting mold as shown on the right side in  FIG. 2 . 
         [0060]    Since highly pure silicone without any admixture of adhesion promoter in the silicone is used in the present case, no further measures aimed at releasing the silicone  3  from the mold  6  are required. In particular, the casting mold is not being lined with a release film or the like. This simplifies the production and enables very exact reproduction of the structures of the casting mold. 
         [0061]    The method described above can be applied repeatedly to the same object, if required.  FIG. 5  and  FIG. 6  show embodiments of the invention, which each show such refinements of examples from  FIG. 4 . In each case, after producing a first layer  3  having optical elements  4 , a second layer  3 ′ having optical elements  4 ′ was produced. 
         [0062]    In the case of the example according to  FIG. 5 , the second layer  3 ′ was applied onto the back side and/or opposite sides of the substrate  1 , which is provided as a planar plate in the present case. For this purpose, the substrate simply needs to be provided with an adhesion promoter  2  on the yet uncoated side  9  and then inserted forward in a corresponding casting mold  6 . The further procedural steps correspond to the procedure described above. 
         [0063]    In the example shown in  FIG. 5 , the first surface  5 , which is the front side of the substrate  1 , has been coated with a plurality of collecting lenses  4  for purposes of illustration. The second surface  9 , which is the back side of the substrate  1 , has been coated with Fresnel lenses  4 ′ which each are aligned with the collecting lenses  4 . 
         [0064]    In the example shown in  FIG. 6 , first a layer  3 , having Fresnel lenses in the present case, was applied to the first surface  5 , which is the front side of the substrate. Subsequently, an adhesion promoter  2  was applied onto the layer  3  and a second layer  3 ′ having collecting lenses  4 ′ was then applied onto the first layer  3 . In this case, the first layer  3  applied is the substrate according to the scope of the invention and its external surface is the second surface  9 . 
         [0065]    As a matter of principle, the number and design of such multiple layers are not limited in any way. 
         [0066]    The layers can just as well differ in composition of the casting material, in particular be different casting materials and/or admixtures to the casting materials. Accordingly, different properties can thus be combined or the optical properties obtained by application of many layers can be influenced nearly gradually, e.g. by slightly changing the refractive index of the casting material used. Likewise, the final current boundary layer can be influenced and changed before applying the next layer, e.g. by silanizing a silicone boundary layer, dielectric or metallic coating by sputtering, spraying, wetting, or any other customary surface coating procedures. 
         [0067]    The use of particularly pure silicone is specified above as being preferred in order to optimize high degrees of transmission and material resistance in critical wavelength ranges. As a matter of principle, the casting material can be filled with optically effective materials in order to thus generate further optical functionalities, such as conversion of the wavelength of light by introducing phosphorescent and fluorescent substances, such as rare earth elements, or for affecting the opacity of the optical system by introducing scattering substances, such as transparent or translucent particles (e.g. made of glass or ceramic materials) or metallic particles. 
         [0068]      FIG. 7  shows a preferred use of an optical system  10 , as described above, in combination with a two-dimensional light source. The light source is provided in this case as LED module  11  having a number of LEDs arranged in an array. The optical system is situated at a distance in front of the light source and refracts the light of the individual LEDs in desired manner, by collecting lenses that are each assigned to one LED. 
         [0069]      FIG. 8  shows another preferred use, in which a module according to the invention embodiment according to  FIG. 1  is combined with a module according to the invention embodiment according to  FIG. 4 . Overall, a first optical module is present that is provided as LED module  1 ,  1   a,    1   b  having a primary optical system  3 . A second optical module provided as optical system  10  is arranged upstream of the first optical module. Preferably, both modules comprise multiple collecting lenses, each correlated to the LEDs, which act in concert to transport a large opening angle of the LEDs. 
         [0070]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.