Polymeric blend with high resistance to fuel
FIELD OF THE INVENTION 
     The present invention relates to a new polymeric blend and to a fuel container and particularly a fuel hose made of this blend. 
     PRIOR ART 
     It is known that nylon 6 and nylon 6,6 cannot be reliably used to make fuel hoses and particularly gasoline hoses because these materials do not withstand dissolving action of ZnCl 2  or CaCl 2  as specified by major automotive industries. It was noted that the lower resistance occurs in the areas in which a hose is bent. In fact the bending causes a local higher mechanical stress which decreases the fuel resistance. 
     Nylon compounds with a higher carbon atom number, such as nylon 11 and nylon 12 have a better resistance, but they are much more expensive and above all are not flexible without plasticizers. However plasticizers cannot be used because they are extracted by gasoline which is a very good solvent of plasticizers. 
     Nylon 6,36 is much more flexible, but also this compound has about the same poor fuel resistance, of nylon 6. 
     It is also known that the blending of nylon 6 or nylon 6,6 with other polymeric compounds with the aim of improving flexibility or fuel resistance gives rise to blending problems since the blending compatibility of nylon 6 and nylon 6,6 is very poor. 
     SUMMARY OF THE INVENTION 
     According to the present invention, it is hereby surprisingly provided a blend having improved resistance to fuel, comprising: 
     (a) a copolymer obtainable from copolymerization of ε-caprolactam, and a substance selected from the group consisting of: 
     an aminocarboxylic acid having a carbon atom number not lower than 9, 
     a lactam corresponding to said aminocarboxylic acid and 
     a mixture of hexamethylenediamine with a dicarboxylic acid having a carbon atom number not lower than 9; 
     (b) a polyolefin polymer with functional groups selected from the group consisting of carboxyl groups, esters, anhydrides and carboxylates. 
     Preferably a weight ratio of component (a) with respect to component (b) is of from 0.25 to 4 and more preferably said weight ratio is of from 0.65 to 2.5. 
     Preferably a weight ratio of said ε-caprolactam with respect to said hexamethylenediamine plus said dicarboxylic acid is of from 1.5 to 19 and more preferably said weight ratio is of from 4 to 9. 
     Preferably said carbon atom number is not lower than 10 and more preferably is 11 or 36. 
     Preferably said polyolefin polymer is selected from the group consisting of ethylene acrylic acid copolymer and ethylene acrylic acid ester copolymer. 
     Preferably said polyolefin polymer is from 0.1% to 20% with respect to the total weight of said blend. 
     Preferably said ethylene ethyl acrylate is from 5% to 15% with respect to the total weight of said blend. 
     Preferably said polyolefin polymer is anionomer, more preferably said ionomer is from 0.1% to 20% with respect to the total weight of said blend, still more preferably said ionomer is from 5% to 15% with respect to the total weight of said blend. 
     Preferably said polyolefin polymer is ethylene-propylene functionalized with maleic anhydride, more preferably said ethylene-propylene functionalized with maleic anhydride is from 0.1% to 30% with respect to the total weight of said blend, still more preferably said ethylene-propylene functionalized with maleic anhydride is from 5% to 25% with respect to the total weight of said blend. 
     Preferably the blend according to the invention comprises also nylon 6 in an amount of from 0.1% to 20% with respect to the total weight of said blend, more preferably said amount is of from 0.1% to 7%. 
     Preferably the blend according to the invention comprises also nylon 12 in an amount of from 0.1% to 40% with respect to the total weight of said blend, more preferably said amount is of from 0.1% to 25% acrylate. 
     Preferably said polyolefin polymer is ethylene ethyl acrylate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following examples disclose the invention, but do not have any limitative effect. Parts are intended by weight, unless otherwise specified. 
     EXAMPLE 1 
     The copolymerization conditions for preparing the copolymer which forms component (a) of the blend according to the invention are the following with reference to a dicarboxylic acid having a carbon atom number of 36. 
     A stoichiometrically balanced solution of hexamethylene diamine and dimer acid in caprolactam is prepared; the weight ratio of hexamethylene diamine to caprolactam being 0.033. 0.47% by weight (based on caprolactam) of azelaic acid is added as molecular weight regulator. 2.0% of water is added. 
     The solution is copolymerized in a stirred, heated autoclave at atmospheric pressure with a nitrogen purge for 7 hours or until a melt temperature of 250° C. is reached. 
     Pressure is gradually reduced to 100 Torr absolute until the desired viscosity is reached. The preferred relative viscosity is in the range of from 2.5 to 3.5. Viscosity is determined through measurement of agitator speed and hydraulic pressure required to turn agitator. 
     EXAMPLE 2 
     The copolymerization conditions for preparing the copolymer which-forms component (a) of the blend according to the invention are the following with reference to a dicarboxylic acid having a carbon atom number of 11. 
     A mixture of 1 part aminoundecanoic acid slurry in approximately 5.7 parts of molten caprolactam is prepared. 
     The mixture is copolymerized in a stirred, heated autoclave at atmospheric pressure with a nitrogen purge for 7 hours or until a melt temperature of 250° C. is reached. 
     Pressure is gradually reduced to 100 Torr absolute until the desired viscosity is reached. Viscosity is determined through measurement of agitator speed and hydraulic pressure required to turn agitator. 
     EXAMPLES 3-12 
     The blend according to the invention is prepared using an Essex single screw extruder with I.D. of 1.5 inch. The screw is a single stage screw with a ratio L/D of 24/1 and compression ratio) of 3.5/1. The screw speed is of from 10 to 35 rpm depending on the capability of the compounding equipment. 
     The screen packs are in sequence from small number of mesh to large number of mesh and particularly 60-120-240-120, etc. The type of extruder, compounding equipment and screw design is flexible, as long as the equipment produce good mixing product. 
     The temperature in the bopper, extruder and die is in the range of from 233° to 288° C. The preferred temperature in the hopper is 244° C. The preferred temperature of the blend at the outlet of the extruder is 266° C. The preferred temperature in the extruder is in the range of 255° to 266° C. 
     The compositions of examples 3-12 are reported in the table. Particularly the last two lines of the table report the time required for dissolving the final product in ZnCl 2  at respectively 23° and 700° C. The test with ZnCl 2  is important because is particularly reliable to assess the general resistance to fuel, since the behaviour of a polymer with ZnCl 2  is comparable with the behaviour of the same polymer with fuel. 
     
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Examples    3  4  5  6  7  8  9  10 11 12
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copolymer:  65 45 35 -- -- -- 100
                                 -- -- --
ε-caprolactam,
hexamethylenediamine,
oleic acid dimer
copolymer:  -- -- -- 65 45 35 -- 100
                                    -- --
ε-caprolactam,
amine-undecanoic
acid
ethylene    10 10 10 10 10 10 -- -- -- --
ethyl acrylate
ionomer     10 10 10 10 10 10 -- -- -- --
ethylene-propylene
            10 20 15 10 20 15 -- -- -- --
functionalized with
maleic anhydride.
nylon 6     5  5  5  5  5  5  -- -- 100
                                       --
nylon 12    -- 10 25 -- 10 25 -- -- -- 100
stab/additives
            0.2
               -- 0.2
                     0.2
                        -- 0.2
                              -- -- -- --
ZnCl.sub.2 23° C.
            1000
               1000
                  1000
                     1000
                        1000
                           1000
                              25 20 5  500
            hr hr hr hr hr hr min
                                 min
                                    min
                                       hr
ZnCl.sub.2 70° C.
            200
               170
                  200
                     200
                        170
                           200
                              NA NA NA NA
            hr hr hr hr hr hr
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