Abstract:
A hardenable reaction resin system, in particular a casting compound, laminating resin, or impregnating resin, which is to be processed as a two-component compound and contains a resin component, a mineral filler, and polymer particles dispersed in the resin component. The filler includes nanoparticles.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a hardenable reaction resin system, a method for manufacturing same, as well as its use.  
       BACKGROUND INFORMATION  
       [0002]     Systems based on a resin which hardens via a chemical reaction play a significant role in the manufacture of industrial components. When such reaction resin systems are used for insulation purposes, they usually have a high filler content. High filler contents result in a high thermal and mechanical resistance of the hardened reaction resin systems.  
         [0003]     German Patent Application No. DE 100 51 051 describes such epoxy resin-based reaction resin systems. They contain up to 75 wt. % filler. Higher filler contents are impossible to implement in the systems described therein, because they would have a negative effect on the viscosity, i.e., processability of the casting compound.  
         [0004]     An object of the present invention is to provide a hardenable reaction resin system which has a high thermal and mechanical resistance, yet is easy to process.  
       SUMMARY OF THE INVENTION  
       [0005]     The object of the present invention is achieved by providing a reaction resin system which is usable as a two-component system and contains nanoparticles as a filler. By using nanoparticles as a filler, reaction resin systems having up to 90 wt. % filler content, yet being castable, are achievable.  
         [0006]     When hardened, the reaction resin system has low linear shrinkage and is characterized by a higher elongation at rupture and a low thermal expansion coefficient.  
         [0007]     Furthermore, the reaction resin system preferably has fused silica or silica flour particles as a filler, which results in a particularly pronounced thermal stability, a low expansion coefficient, and a low dielectric constant.  
         [0008]     In a particularly advantageous embodiment, the reaction resin system has bisphenol A, bisphenol B, and/or bisphenol F, optionally mixed with an epoxy, as the resin component. This resin system has a high degree of cross-linking and therefore high mechanical stability when hardened. 
     
    
     DETAILED DESCRIPTION  
       [0009]     A reaction resin system according to the present invention has three basic components: a resin component A, a filler B, and polymer particles C, which are dispersed in resin component A. In addition, at least one hardener D and commonly used additives are provided such as one or more antifoaming agents, sedimentation inhibitors, or adhesion promoters.  
         [0010]     In general, it should be kept in mind that the reaction resin system must form a stable system before and during processing to prevent the components from separating. Thus, filler particles B and polymer particles C should form stable dispersions with resin component A, and, if there are more resin components A, resin components A should form stable solutions or emulsions among themselves. This stability must be ensured during both processing and hardening of the reaction resin system.  
         [0011]     Basically a plurality of monomers, cross-linkable compounds, or mixtures of such compounds may be used as resin component A. Particularly advantageous is the use of compounds having at least one epoxy function, optionally mixed with other compounds with or without an epoxy function. Thus, for example, diepoxides, triepoxides, or tetraepoxides are suitable; the commercially available compounds mentioned in the following are provided as examples. Cycloaliphatic, preferably ring-epoxidized diepoxides, such as (I) and (VI) have been found particularly suitable.  
                         
                         
 
         [0012]     Resin component A may include one or more of compounds (I) to (VII) or other resin components. Alternatively, resin components based on bisphenol A, bisphenol B, and/or bisphenol F, PUR, or cyanate esters alone or in mixtures with one another or with suitable epoxy resin components may be used.  
         [0013]     Furthermore, a novolak epoxy resin may be used as resin component A, in particular a cresol-novolak epoxy resin of the following composition:  
                         
 
         [0014]     Resin component A is contained in the reaction resin system in a proportion of 5% to 95 wt. %, preferably 10% to 60 wt. %, in particular 12% to 28 wt. %.  
         [0015]     The reaction resin system also contains a filler B, which, if appropriately selected, reduces the shrinkage of the hardened reaction resin system and increases the thermal stability and tear resistance of the hardened reaction resin system. Filler B contains nanoparticles, nanoparticles being understood as a particle fraction whose mean grain size distribution d 50 is in the nanometer range. Aluminum oxide, chalk, silicon carbide, boron nitride, carbon black, and talcum, for example, are suitable as fillers. Filler B preferably has particles of silica flour (powder) or fused silica or mixtures of same. In a particularly preferred embodiment, filler B has particles of two different grain size distributions d 50 . A first part of the filler particles is characterized by a grain size distribution in the nanometer range, and a second part of filler particles is preferably characterized by a grain size distribution d 50  preferably in the micrometer range.  
         [0016]     By using nanoparticles, the overall proportion of filler B in the reaction resin system may be increased to 90 wt. %, the reaction resin system still remaining sufficiently fluid during processing and hardening. The total filler content in the reaction resin system may thus equal 2% to 90 wt. %, preferably 50% to 70 wt. %, in particular 2% to 25 wt. %.  
         [0017]     The use of silanized filler particles has been found to be particularly suitable, because the modification of the filler particle surfaces ensures improved bonding of filler B to resin matrix A of the reaction resin system. To be able to set the degree of silanization of filler B, either the filler is previously treated with a silanizing agent and the presilanized filler is mixed into the reaction resin system, or the silanizing agent is added to the reaction resin system and the actual silanization reaction takes place in the reaction resin system. Alternatively, filler B may also have a chemically modified surface in the form of a polymer layer, of PMMA, for example (known as core shell particles).  
         [0018]     The reaction resin system also contains polymer particles dispersed in resin component A as third component C. These are polysiloxane-containing polymers in particular, component C preferably representing a dispersion of one or more silicones in resin component A. Preferably silicone particles in the form of silicone resin particles or silicone elastomer particles having a particle diameter of 10 nm to 100 μm are used. Basically, the silicone particles may have a chemically modified surface in the form of a polymer layer, for example, of PMMA (known as core shell particles); however, it has been found that untreated or surface-functionalized silicone particles are better suited for achieving the object of the present invention. Alternatively, elastomer particles of acrylonitryl-butadiene-styrene copolymerizate (ABS) are also suitable.  
         [0019]     The reaction resin system contains up to 25 wt. %, preferably up to 10 wt. % of polymer particles C.  
         [0020]     To ensure that the reaction resin system as a two-component system is processable, a hardener is also provided. Hexahydrophthalic acid anhydride or methyl nadic acid anhydride (MNSA), for example, are suitable for this purpose.  
         [0021]     The present reaction resin system may be used either as an impregnating resin or as a casting compound. For processing as an impregnating resin, for impregnating electrical windings, for example, the winding to be impregnated is rotated, and either immersed into the liquid impregnating resin or the liquid impregnating resin is dripped onto the rotating winding. The impregnated winding is hardened thermally, for example, or via UV-supported cross-linking.  
         [0022]     If the reaction resin system is used as a casting compound, casting to form a molded part is performed at a higher temperature. When the reaction resin system is heated to the appropriate temperature, it has such a low viscosity and such a high capillary effect that it may be cast even into unfavorable geometries, such as casting gaps having a diameter of &lt;300 μm. This makes very short cycle times possible at the same time. The cast reaction resin system is exposed to a temperature of 60° to 110° C. for 30 to 300 minutes or a temperature of 120° C. for 10 to 100 minutes to achieve gelling of the reaction resin system. Subsequently it is exposed to a temperature of 140° to 220° C. for 10 to 90 minutes to harden the molded part.  
         [0023]     The following exemplary embodiments of reaction resin systems present their compositions (in wt. %) and the resulting properties after hardening. Exemplary embodiments 1, 2, 6, and 7 are reference samples containing no polymer particles C or nanoparticles as filler B.  
         [0000]     1. Resin component A corresponds to a cycloaliphatic epoxide.  
         [0024]     Compositions  
                                                                                                   Exemplary Embodiment                1   2   3   4   5                        Resin component A   16.96   45.9   13.52   12.53   18.3       Cycloaliphatic epoxide       Filler B   62.52   —   62.87   57.9   49.97       Fused silica       Filler B   —   —   3.65   3.38   5.0       Fused silica nanoparticles       Polymer particles C   —   —   3.65   3.39   5.0       Silicone elastomer       Additives   0.59   —   0.34   0.318   0.08       Hardeners   19.93   54.1   15.97   14.78   21.65                  
 
         [0025]     The above compositions resulted in the following property profile:  
                                                                                                   Exemplary Embodiment                1   2   3   4   5                        Viscosity at   2800   34   5160   13000   1500       60° C. [mPa*s]       Linear   −0.3   −0.2   0.15   0.15   0.1       shrinkage       [%]       Glass   230   —   239   226   180       transition       temperature       [° C.]       Thermal   32-35   67   23   21   35       expansion       coefficient       [10 −6 *1/° C.]       E-module   8990/   2890/   9750/   10360/   6730/       bending/   10200   2900   10390   11060   6410       tensile test       [N/mm 2 ]       Tension at   104/61   124/40   108/72   98/64   107/68       rupture/tear       [N/mm 2 ]       Elongation at   1.0/   5.4/   1.24/   1.05/   1.76/       rupture/tear   0.62   1.46   0.91   0.73   1.26       [%]                  
 
 II. Resin component A corresponds to a bisphenol A resin. 
 
         [0026]     Compositions  
                                                                                       Exemplary Embodiment                6   7   8                            Resin component A   51.5   25.73   20.6           Bisphenol A           Filler B Fused silica   —   —   49.9           Filler B Fused silica   —   49.92   4.99           nanoparticles           Polymer particles C   —   —   4.99           Silicone elastomer           Additives   —   0.16   0.18           Hardeners   48.5   24.19   19.34                      
 
         [0027]     The above compositions resulted in the following property profile:  
                                                                                   Exemplary Embodiment                6   7   8                        Viscosity at 60° C. [mPa*s]   51   —   1630       Linear shrinkage [%]   0.7   —   0.36       Glass transition temperature   149   —   133       [° C.]       Thermal expansion   66   —   33       coefficient [10 −6 *1/° C.]       E-module bending/tensile test   2920   6930/7050    9000/75400       [N/mm 2 ]       Tension at rupture/tear   130/55    144/89    149/73        [N/mm 2 ]       Elongation at rupture/tear [%]   9.39/2.45   2.47/1.79   2.06/1.65                  
 
         [0028]     Due to its thermal stability when hardened, the reaction resin system is suitable primarily for components exposed to temperatures up to 240° C., at least from time to time.  
         [0029]     The reaction resin system according to the present invention thus may be used, for example, for casting diodes, ignition coils, or electronic components. Furthermore, electric windings may be impregnated using the reaction resin system.