The present invention describes a polyamide-rubber blended composition having improved resistance to ozone, stress whitening and gasoline prepared by mixing together with heating the following components: PA1 (a) from 70 to 20 volume percent of a rubber composition consisting of: PA2 (i) 30 to 70 volume percent of an acrylonitrile-butadine copolymer rubber containing at least 0.8 weight percent of an epoxy group in the polymer, and PA2 (ii) 30 to 80 volume percent of an epichlorohydrin rubber; PA1 (b) 30 to 80 volume percent of a polyamide resin; and PA1 (c) at least 0.15 parts by weight of a carboxylic acid having a functional group calculated in terms of the weight of the carboxyl group per 100 parts by weight of the rubber composition of component (a).

FIELD OF THE INVENTION 
The present invention relates to a polyamide-rubber blended composition 
having improved characteristics with respect to strength, flexibility and 
resistance to ozone, stress whitening and gasoline. 
BACKGROUND OF THE INVENTION 
Polyamide resins are recently attracting the attention of researchers as 
materials for producing more durable and lighter automotive hopes such as 
gasoline supply hoses. However, since polyamide resin hoses are not as 
flexible as rubber hoses, efforts are being made to provide high 
flexibility to the polyamide resins by one of the following three methods: 
the addition of a plasticizer to the polyamide resin; blending rubber with 
the polyamide resin; and block and/or graft polymerizing a dissimilar 
monomer onto the polyamide resin. However, the use of a plasticizer is not 
practically feasible because the plasticizer vaporizes with heat or is 
extracted with gasoline and other oils or solvents, causing a significant 
drop in the flexibility of the polyamide resin. The block and/or graft 
copolymer prepared by the third method has a low melting point and is not 
suitable for high-temperature use which is the principal intended 
application of the polyamide resin. 
In order to permit use in applications where contact with gasoline and 
other oils or solvents is expected, the rubber for use as a component to 
be blended with the polyamide resin in the second method is selected from 
acrylonitrile-butadiene copolymer rubber (for convenience this will simply 
be referred to as nitrile rubber) and epichlorohydrin rubber (hereunder 
simply referred to as hydrin rubber). Japanese patent publication No. 
14096/1980 and U.S. Pat. No. 4,173,556 show a method in which a blend of 
the nitrile rubber and polyamide resin is mixed with a cross-linking agent 
with heating so that the nitrile rubber is dispersed in the polyamide 
resin while the rubber is being cross-linked. Similarly, Japanese patent 
application (OPI) No. 5753/1982 and U.S. Pat. No. 4,297,453 show a method 
in which a blend of the hydrin rubber and polyamide resin is mixed with a 
cross-linking agent with heating so that the hydrin rubber is dispersed in 
the polyamide resin while the rubber is being cross-linked. However, the 
nitrile rubber impairs significantly an inherent high resistance to 
thermal aging of the polyamide resin, further the hydrin rubber reduces 
the good strength properties of the polyamide resin. 
The present inventors previously proposed in Japanese Patent application 
No. 41576/1983 (corresponding to U.S. patent application Ser. No. 589,223 
filed on Mar. 13, 1984) a method for preventing the drop in the resistance 
to thermal aging and strength properties of a polyamide resin by blending 
a polyamide resin with two other polymers, i.e., nitrile rubber and hydrin 
rubber. However, the resulting blend is inferior to the polyamide resin 
per se in respect to resistance to ozone, upon the Cyclic application of 
large strains, and resistance to stress whitening under appreciable local 
strains. Therefore, this three-polymer blend is not satisfactory for use 
for parts which are subject to significant vibrations or extreme strains. 
Therefore, the present inventors continued their studies on producing a 
polyamide-rubber blended composition which has improved resistance to 
ozone and stress whitening, as well as high strength and flexibility, and 
significant resistance to thermal aging as well as gasoline. As a result, 
it has been found that the desired composition can be produced by the 
present invention. 
SUMMARY OF THE INVENTION 
The primary purpose of the present invention is to provide a 
polyamide-rubber blended composition having improved resistance to ozone 
and stress whitening, as well as high strength and flexibility, and 
substantial resistance to thermal aging and gasoline. 
The polyamide-rubber blended composition of the present invention is 
prepared by mixing the following components under heating: 
(a) 70-20 vol% of a rubber composition consisting of (i) 30-70 vol% of an 
acrylonitrile-butadiene copolymer rubber containing at least 0.8 wt% of an 
epoxy group in the polymer and (ii) 70-30 vol% of an epichlorohydrin 
rubber; 
(b) 30-80 vol% of a polyamide resin; 
(c) at least 0.15 parts by weight of a carboxylic acid having a functional 
group in terms of the weight of the carboxyl group per 100 parts by weight 
of the rubber composition specified in (a). 
DETAILED DESCRIPTION OF THE INVENTION 
The epoxy containing nitrile rubber (hereunder referred to as epoxy nitrile 
rubber) in component (a) of the composition of the present invention is a 
copolymer of acrylonitrile, butadiene and an epoxy containing monomers 
such as glycidyl acrylate, glycidyl methacrylate, vinyl glycidyl ether, 
allyl glycidyl ether, methaglycidyl ether or glycidyl ethers of 
hydroxyalkyl acrylates or hydroxyalkyl methacrylates, or a mixture thereof 
or a copolymer wherein acrylonitrile and butadiene is the major components 
are polymerized with an acrylate ester or isoprene and the 
epoxy-containing monomer. In either case, the epoxy nitrile rubber 
contains not less than 0.8 wt% of the epoxy group in the rubber. If the 
content of the epoxy group is less than 0.8 wt%, the resulting 
polyamide-rubber blended composition has an undesirably low resistance to 
ozone and stress whitening. It is preferred that the epoxy nitrile rubber 
has a bound acrylonitrile content of 10-55 wt% and a glass transition 
point of 10.degree. C. or less, and those having the bound acrylonitrile 
content of 30-50 wt% are particularly preferred in view of compatibility 
with the epichlorohydrin rubber to be mixed. 
The epichlorohydrin rubber in component (a) of the composition of the 
present invention may be a homopolymer of epichlorohydrin, copolymer of 
epichlorohydrin and ethylene oxide, a copolymer of epichlorohydrin and 
propylene oxide, or a terpolymer of epichlorohydrin, ethylene oxide or 
propylene oxide and allylglycidyl ether. 
If the rubber composition of component (a) consisting of the epoxy nitrile 
rubber and epichlorohydrin rubber is less than 20 vol% of the total volume 
of the rubber composition and the polyamide resin, the effect of the 
rubber composition's improvement of the flexibility of the polyamide resin 
is not exhibited to the fullest extent. If the proportion of the rubber 
composition exceeds 70 vol%, the thermoplasticity of the polyamide resin 
is impaired and the resulting blend has poor processability. 
The polyamide resin as component (b) of the composition of the present 
invention is a crystalline thermoplastic resin having an amino bond in the 
polymer. Examples of this polyamide resin are homopolymers such as 
polycaprolactam (nylon 6) and polylauryllactam (nylon 12), and copolymers 
such as the condensation polymer of 11-aminoundecenoic acid (nylon 11), 
polyhexamethylene azelamide (nylon 6,9) and polyhexamethylene sebacamide 
(nylon 6,10), as well as polyamide resins prepared by block and/or graft 
copolymerization of these comonomers with other monomers. preferred 
polyamide resins are those onto which a dissimilar monomer is block and/or 
graft polymerized in such an amount that it does not greatly reduce the 
melting point of the polyamide resin. 
The proportions of the epoxy nitrile rubber and hydrin rubber to be blended 
to form the rubber compositions (a) or (c) are such that the epoxy nitrile 
rubber is 30-70 vol%, preferably 40-60 vol%, of the total volume of the 
two rubbers, and the hydrin rubber is 70-30 vol%, preferably 60-40 vol%, 
on the same basis. If the epoxy nitrile rubber is more than 70 vol% or 
less than 30 vol%, the ozone resistance of the final composition is 
appreciably reduced. If the amount of the epoxy nitrile rubber is less 
than 30 vol%, the resistance to stress whitening of the composition is 
also decreased by a significant degree. 
The polyamide-rubber blended composition of the present invention may 
contain carbon black, white filler, plasticizer and processing aid(s) for 
the purpose of providing further improved strength and processability. If 
desired, the composition may also contain various additives such as 
stabilizers and color pigments which are commonly used with resins and 
rubbers. 
Illustrative carboxylic acids having a functional group that are used in 
the blended composition of the present invention include aliphatic 
dicarboxylic acids such as adipic acid, aromatic dicarboxylic acids such 
as phthalic acid, polyvalent carboxylic acids such as trimellitic acid, 
amino acids such as 6-amino-n-caproic acid, thiolic acids such as 
thioglycollic acid, and acid anhydrides such as maleic anhydride and 
phthalic anhydride. These carboxylic acids must be added in an amount of 
at least 0.15 part by weight in terms of the weight of the carboxyl group 
for 100 parts by weight of rubber composition (a). If the amount of the 
carboxylic acid component is less than 0.15 parts by weight in terms of 
the carboxyl group, the resulting polyamide-rubber blended composition has 
a significantly decreased processability. 
Components (a), (b) and (c) are conveniently blended in any of the devices 
that permit controlled heating at temperatures higher than the melting 
point of the polyamide resin (b), such as Banbury mixer, pressure kneader, 
Brabender mixer, kneader extruder and heat transfer rolls. After heating 
the devices employed to a temperature higher than the melting point of the 
polyamide resin, this resin, as well as the epoxy nitrile rubber, hydrin 
rubber, carboxylic acid having a functional group and any suitable 
additives are charged into the vessel and kneaded until a homogeneous 
blended composition is obtained. 
In a more preferred embodiment, the epoxy nitrile rubber and hydrin rubber 
are kneaded in a common rubber mixer such as a Banbury mixer, open rolls, 
pressure kneader or Brabender mixer, and thereafter, the polyamide resin 
is blended into the rubber mixture under heating in the presence of the 
carboxylic acid having a functional group. This method is effective for 
providing a blended composition having further improved resistance to 
ozone and stress whitening. If desired, the carboxylic acid having a 
functional group may be mixed with the polyamide resin simultaneously with 
the epoxy nitrile rubber and hydrin rubber.