Self-adhesive prepreg face sheets for sandwich panels

Abstract

Resin compositions are provided which are used in combination with fibers to form self-adhesive prepreg sheets that are applied to core materials to form sandwich panels. The prepreg resin includes a thermoset resin, a curing agent and a viscosity control agent. The prepreg resin further includes certain thermoplastic particles which are used to control the flow characteristics of the prepreg resin and the formation of fillets during bonding of the prepreg to the core material.

What is claimed is:  
     
         1 . A self-adhesive prepreg for bonding to a honeycomb, said self-adhesive prepreg comprising: 
 at least one fiber layer;    a resin which has been combined with said fiber layer to form a prepreg which includes a bonding surface that is adapted to be bonded directly to said honeycomb, said resin comprising a thermoset resin, a curing agent and a sufficient amount of a viscosity control agent to provide a resin having a viscosity which is sufficient to allow said resin to be combined with said fiber layer to form said prepreg; and    thermoplastic fillet forming particles which are incorporated into said resin in an amount sufficient to form a prepreg resin which is self-adhesive and wherein said fillet forming particles are not dissolved to a substantial degree in said prepreg resin.    
     
     
         2 . A self-adhesive prepreg according to  claim 1  wherein said thermoset resin is selected from the group consisting of epoxy and cyanate ester resins.  
     
     
         3 . A self-adhesive prepreg according to  claim 1  wherein said thermoplastic fillet forming particles are selected from the group consisting of densified and micronized thermoplastic particles which have a glass transition temperature that is above 200° C.  
     
     
         4 . A self-adhesive prepreg according to  claim 1  wherein said thermoplastic fillet forming particles are selected from the group consisting of densified polyether sulfone, micronized polyether sulfone and densified polyetherimide.  
     
     
         5 . A self-adhesive prepreg according to  claim 3  wherein said thermoplastic fillet forming particles have particle sizes ranging from 1 to 100 microns.  
     
     
         6 . A self-adhesive prepreg according to  claim 1  wherein said prepreg resin comprises an epoxy thermoset resin, a polyetherimide or polyethersulfone viscosity control agent and densified polyether sulfone fillet forming particles.  
     
     
         7 . A self-adhesive prepreg according to  claim 1  wherein the minimum viscosity of said prepreg resin over the curing temperature range of said prepreg resin is between 150 to 1500 poise.  
     
     
         8 . A self-adhesive prepreg according to  claim 1  wherein the minimum viscosity of said prepreg resin over the curing temperature range of said prepreg resin is between 300 to 1200 poise.  
     
     
         9 . A self-adhesive prepreg according to  claim 1  wherein said thermoplastic fillet forming particles are located substantially at said bonding surface of said prepreg.  
     
     
         10 . A cured honeycomb panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 1  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin.  
     
     
         11 . A cured honeycomb panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 3  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin.  
     
     
         12 . A cured honeycomb panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 5  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin.  
     
     
         13 . A cured honeycomb panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 6  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin.  
     
     
         14 . A cured honeycomb panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 7  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin.  
     
     
         15 . A cured honeycomb panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 8  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin.  
     
     
         16 . A cured honeycomb panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 9  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin.  
     
     
         17 . A method for adhesively bonding a prepreg face sheet to a honeycomb comprising the steps of: 
 forming a self-adhesive prepreg comprising providing at least one fiber layer and a prepreg resin wherein said prepreg resin is combined with said fiber layer to form a prepreg resin layer comprising a bonding surface which is adapted to be bonded directly to said honeycomb, said prepreg resin comprising a thermoset resin, a curing agent and a sufficient amount of a viscosity control agent so that said prepreg resin has a viscosity which is sufficient to allow said prepreg resin to be combined with said fiber layer to form said prepreg resin layer, said step of forming a self-adhesive prepreg further including the step of incorporating thermoplastic fillet forming particles into said prepreg resin in an amount sufficient to form a prepreg layer which is self-adhesive and wherein said fillet forming particles are not dissolved to a substantial degree in said prepreg resin;    bonding said self-adhesive prepreg to said honeycomb wherein said bonding comprises curing said self-adhesive prepreg for a sufficient time and at a sufficient temperature to substantially dissolve said fillet forming particles.    
     
     
         18 . A method according to  claim 17  wherein said thermoset is selected from the group consisting of epoxy and cyanate ester resins.  
     
     
         19 . A method according to  claim 17  wherein said thermoplastic fillet forming particles are selected from the group consisting of densified and micronized thermoplastic particles which have a glass transition temperature that is above 200° C.  
     
     
         20 . A method according to  claim 17  wherein said thermoplastic fillet forming particles are selected from the group consisting of densified polyether sulfone, micronized polyether sulfone and densified polyetherimide.  
     
     
         21 . A method according to  claim 18  wherein said thermoplastic fillet forming particles have particle sizes ranging from 1 to 100 microns.  
     
     
         22 . A method according to  claim 17  wherein said prepreg resin comprises an epoxy thermoset resin, a polyetherimide or polyethersulfone viscosity control agent and densified polyether sulfone fillet forming particles.  
     
     
         23 . A cured honeycomb sandwich panel comprising a core having at least one face to which a self-adhesive prepreg according to  claim 1  is bonded and wherein said thermoplastic fillet forming particles are substantially dissolved in said prepreg resin and wherein said honeycomb exhibits a core crush of less than 5%.  
     
     
         24 . A cured honeycomb sandwich panel according to  claim 23  wherein said fabric layer comprises 6K or 12K carbon fabric.  
     
     
         25 . A cured honeycomb sandwich panel according to  claim 24  wherein said fabric layer comprises 6K or 12 K carbon fabric and said honeycomb exhibits a core crush which is essentially 0%.