Polyamide-Rubber Blended Composition

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.

Polyamide resins are recently attracting the attention of researchers as materials for producing more durable and lighter automotive hoses 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 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 properites of the polyamide resin.

The present inventors previously proposed in Japanese Patent Application No. 41576/1983 (corresponding to U.S. 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 of 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.

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 comprises:

(a) 70-20 vol% of a rubber composition consisting of (i) 30-70 vol% of an acrylonitrile-butadiene copolymer rubber containing at least 0.7 wt% of a carboxyl group in the polymer and (ii) 70-30 vol% of an epichlorohydrin rubber;

(b) 30-80 vol% of a polyamide resin;

(c) at least 0.1 parts by weight of a polyepoxy compound in terms of the weight of the epoxy group per 100 parts by weight of the rubber composition specified in (a).

provided that components (a) and (b) are mixed first, followed by the addition of component (c), and the resulting mixture then is kneaded under heating.

The carboxyl-containing nitrile rubber (hereunder referred to as carboxyl nitrile rubber) in component (a) of the composition of the present invention is a copolymer of acrylonitrile, butadiene and a carboxyl containing monomer such as methacrylic acid, acrylic acid, maleic acid, or fumaric acid, or a copolymer wherein acrylonitrile and butadiene as the major components are polymerized with acrylate ester or isoprene and the carboxyl containing monomer. In either case, the carboxyl nitrile rubber contains at least 0.7 wt%, preferably not less than 2 wt%, of a carboxyl group in the polymer. If the carboxyl group content in the polymer is less than 0.7 wt%, the ozone resistance of the final composition is appreciably reduced. The carboxyl nitrile rubber preferably has a glass transition point of 10.degree. C. or less and a bound acrylonitrile content of 10-55 wt%, and those having the bound acrylonitrile content of 30-50 wt% are particularly preferred in view of compatibility with an epichlorohydrin rubber.

The epichlorohydrin rubber in component (a) of the composition of the present invention may be a homopolymer of epichlorohydrin, a copolymer of epichlorohydrin and ethylene oxide or 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 carboxyl 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 amido bond in the polymer. Examples of this polyamide resin are hopolymers such as polycaprolactam (nylon 6) and polylauryllactam (nylon 12), and copolymers such as the condensation polymer of 11-aminoundecanoic 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 carboxyl nitrile rubber and hydrin rubber to be blended to form the rubber composition (a) are such that the carboxyl 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 carboxyl 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 carboxyl 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.

Examples of the polyepoxy compound as component (c) of the composition of the present invention include diglycidyl or polyglycidyl ether of bisphenol A, bisphenol F, resorcinol novolak type phenol-formaldehyde or cyclohexanedimethanol, diglycidyl or polyglycidyl ethers of aliphatic polyhydric alcohol such as ethylene glycol, propylene glycol, neopentyl glycol, 1,6-hexanediol, glycerol, trimethylolpropane, diglycerol, polyglycerol or sorbital, or modified compounds thereof such as dibromoneopentyl glycol diglycidyl ether; diglycidyl or polyglycidyl ethers of cyclic compounds such as vinylcyclohexenedioxide; diglycidyl or polyglycidyl esters such as diglycidyl phthalate; oligomers having epoxy groups at their side chains such as polyvinyl glycidyl ether oligomers, polyallyl glycidyl ether oligomers, or polyglycidyl methacrylate oligomers; tri(2,3-epoxypropyl)phosphate; triglycidyl isocyanurate; diglycidyl melamine; and polyglycidyl derivatives. These polyepoxy compounds may be used alone or in combination thereof. Of these, diepoxy compounds of the bisphenol A type; diepoxy compounds such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether and phthalic acid diglycidyl ester; trifunctional and higher-degree functional polyepoxy compounds such as triglycidyl isocyanurate, glycerol polyglycidyl ether and sorbitol polyglycidyl ether are preferably used. These polyepoxy compounds must be added in an amount of at least 0.1 parts by weight, preferably not less than 0.3 part by weight, in terms of the weight of the epoxy group for 100 parts by weight of the rubber composition (a). If the amount of the polyepoxy compound is less than 0.1 parts by weight in terms of the weight of the epoxy group, the resulting polyamide-rubber blended composition has much reduced resistance to ozone and stress whitening.

The preferred polyepoxy compound is such that the cross-linking of the carboxyl nitrile rubber and hydrin rubber is completed by kneading for about 5-30 minutes in the presence of said polyepoxy compound. If the rate of cross-linking of these rubbers is very fast, the rubbers are cross-linked before they are thoroughly dispersed in the polyamide resin, and the homogeniety of the resulting blend composition is significantly impaired. If the rate of cross-linking is too slow, the rubbers are deteriorated.

Components (a), (b) and (c) are 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 these devices to a temperature higher than the melting point of the polyamide resin, this resin, as well as the carboxyl nitrile rubber, hydrin rubber, polyepoxy compound and any suitable additives are charged into the vessel and kneaded until the rubbers are thoroughly cross-linked to provide a homogeneous blended composition.

In a preferred embodiment, the carboxyl 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 mixture under heating in the presence of the cross-linking agent. This method is effective for providing a blended composition having further improved resistance to ozone and stress whitening. mixing the polyepoxy compound with the rubbers before they are blended with the polyamide resin is not preferred because this causes a decrease in the resistance of the final composition to stress whitening and ozone. For example, the polyamide resin is preferably mixed with a premixture of the carboxyl nitrile rubber and hydrin rubber under heating for a period of 5-10 minutes, and thereafter, the polyepoxy compound is added to the mixed blend, and the final mixture is kneaded under heating.

Typical working examples of the present invention as well as Comparative Examples are shown below.

In Examples 1 to 20, the carboxyl nitrile rubbers, hydrin rubbers, and nickel diethyl dithiocarbamate (a stabilizer) listed in Tables 1 to 4 were charged into a Brabender mixer in the proportions indicated. Each formulation was mixed for 5 minutes at a rotor speed of 60 rpm while the temperature in the chamber was held at 60.degree. C.

The resulting rubber compositions and the polyamide resins identified in Tables 1 to 4 were weighed in the proportions listed in the tables, and charged into a Brabender mixer and mixed at a rotor speed of 80 rpm while the temperature in the chamber was held at 190.degree. C. After 10-minute mixing, a polyepoxy compound (a cross-linking agent) was added, whereupon the mixing torque increased to a maximum value and thereafter decreased. The mixing was continued until the torque almost reached a steady value. In Examples 1 to 20, the rubber compositions and the polyamide resins were mixed for 15 minutes after the addition of the polyepoxy compound.

In Comparative Examples 1 to 16, the nitrile rubbers and/or hydrin rubbers and stabilizers shown in Tables 1 to 4 were mixed for 5 minutes in the proportions also shown in Tables 1 to 4. The so prepared rubber compositions where then mixed for 10 minutes under heating with the polyamide resin shown in the Tables. After adding one or more of m-phenylene bis-maleimide, dibenzothiazyl disulfide and Epikote 828 as a cross-linking agent or accelerator, the mixing was continued for an additional 15 minutes. No cross-linking agent was used in Comparative Example 13, wherein the polyamide resin and the rubber composition charged into the mixer were simply kneaded for minutes. The sample of Comparative Example 15 was made of the polyamide resin alone.

The physical properties (tensile strength and elongation at break) of the samples prepared in the Examples and Comparative Examples, as well as their resistance to ozone and stress whitening, are shown in Tables 1 to 4.

The sample of Comparative Example 1 shown in Table 1 was a blended composition of nylon and common carboxyl-free nitrile rubber. Cracks developed in the surface of this sample when it was subjected to 20 hours of cyclic application of 0-30% elongation. This shows that the sample will perform very poorly upon exposure to ozone under hostile conditions.

The sample of Comparative Example 2 was a ternary blended composition of common carboxyl-free nitrile rubber, hydrin rubber and the polyamide resin. The sample of Comparative Example 3 was a blend of the hydrin rubber and the polyamide resin. The sample of comparative Example 4 was a ternary blend of a carboxyl-containing nitrile rubber, hydrin rubber and the polyamide resin. These three samples had a slightly improved ozone resistance as compared with the sample of Comparative Example 1, but the improvement was not as great as desired. Furthermore, the sample of Comparative Example 3 was very low in the resistance to stress whitening.

The samples of Comparative Examples 5 to 10 and Examples 1 to 5 were blended compositions using the carboxy nitrile rubber, hydrin rubber and the polyepoxy compound (as cross-linking agent for the polyamide resin). When the proportion of the hydrin rubber was 70 to 30 vol% of the total volume of the rubber composition as in Examples 1 to 5, the ozone resistance was far better than that obtained in Comparative Examples 1 to 4. The samples of Examples 1 to 5 also had high resistance to stress whitening. However, no improvement in ozone resistance was obtained when the proportion of the hydrin rubber was more than 70 vol% or less than 30 vol% of the total volume of the rubber composition (Comparative Examples 5 to 10).

Table 2 shows the effects of the carboxyl content of the nitrile rubber (Comparative Examples 11 and 12, and Examples 6 and 3), as well as the effects of the amount of polyepoxy compound as the cross-linking agent (Comparative Examples 13 and 14, and Examples 7 to 9 and 3) on the resistance to ozone and stress whitening of the final polyamide-rubber blend composition. When the content of the carboxyl group in the nitrile rubber was less than 0.7 wt% as in Comparative Examples 11 and 12, no great improvement in the ozone resistance was achieved. Furthermore, in Comparative Example 11, the polyamide resin was cross-linked by the polyepoxy compound and the resulting blend was so poorly thermoplastic that its shaping was practically impossible. The samples of Examples 6 and 3 containing more than 0.7 wt% of the carboxyl group in the nitrile rubber exhibited an appreciable improvement in the resistance to ozone and stress whitening. In Comparative Examples 13 and 14, the polyepoxy compound was added in an amount of less than 0.1 parts by weight, in terms of the weight of the epoxy group, per 100 parts by weight of the combination of the carboxyl nitrile rubber and hydrin rubber. The resistance to ozone and stress whitening of the two comparative samples was very low. On the other hand, Examples 7 to 9 and 3 using more than 0.1 parts by weight of the polyepoxy compound in terms of the weight of the epoxy group provided blended compositions having improved resistance to zone and stress whitening.

Table 3 shows the effect of the volume proportion of the rubber composition with respect to the final polyamide-rubber blended composition. When the proportion of the rubber composition was less than 20 vol% of the blend, a high 50% tensile stress occurred and no improvement in the flexibility of the polyamide resin was attained. If the proportion of the rubber composition was more than 70 vol% of the blend (as in Comparative Example 16), the thermoplasticity of the blend was so low as to make its shaping impossible.

Table 4 shows the results of samples according to the present invention using glycidyl terephthalate or triglycidyl isocyanurate instead of Epikote 828 as the cross-linking agent; epichlorohydrin-allyl glycidyl ether copolymer or epichlorohydrin-ethylene oxide copolymer instead of epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer as the hydrin rubber; and nylon 11 instead of nylon 12 as the polyamide resin. All of the modified samples exhibited high resistance to ozone and stress whitening.

The polyamide-rubber blended composition of the present invention provides a product having high flexibility and strength, as well as the significant resistance to ozone, stress whitening, thermal aging and gasoline. Therefore, the composition of the present invention will find extensive use in resin and rubber products in automotive engine compartments and other products that are subjected to great strain due to vibration and which are used at elevated temperatures under exposure to gasoline or gasoline vapor. Com- Com- Com- Com- Com- Com- Com- Com- Com- Com- parative parative parative partative parative parative parative parative parative parative Example Example Example Example Example Example Example Example Example Example Example Example Example Example Example 1 2 3 4 5 6 7 1 2 3 4 5 8 9 10 Composition (parts by weight) Nylon 12*.sup.1 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 Nitrile rubber No. 1*.sup.2 60 30 -- -- -- -- -- -- -- -- -- -- -- -- -- Nitrile rubber No. 4*.sup.3 -- -- -- 30 60 50 45 40 35 30 25 20 15 10 Hydrin rubber No. 1*.sup.4 -- 40 80 40 -- 13 20 27 33 40 47 53 60 67 80 Epikote 828*.sup.5 -- -- -- -- 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Nickel diethyldithiocarbamate 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 m-Phenylenebismaleimide 2 2 2 2 -- -- -- -- -- -- -- -- -- -- -- Dibenzothiazyl disulfide 1 1 1 1 -- -- -- -- -- -- -- -- -- -- -- Stearic acid 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Content of carboxyl group 0 0 -- 0 2.62 2.62 2.62 2.62 2.62 2.62 2.62 2.62 2.62 2.62 -- in nitrile rubber (wt %) Epoxy group content 0 0 0 0 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 (parts by wt.) Polymer composition (vol %)*.sup.6 Overall rubber volume ratio 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 Nitrile rubber volume ratio 100 50 0 50 100 83 75 67 58 50 42 33 25 17 0 Hydrin rubber volume ratio 0 50 100 50 0 17 25 33 42 50 58 67 75 83 100 Initial physical properties* .sup.7 Tensile strength (kg/cm.sup.2) 262 235 121 245 Shaping 248 250 270 230 204 175 144 120 115 Shaping Elongation at break (%) 280 280 200 310 impossible 340 350 350 320 310 260 210 190 180 impossible Ozone resistance*.sup.8 Cracking time (hrs) 20 189 106 136 96 116 320 500 500 212 50 48 Resistance to stress whitening*.sup.9 Percent elongation for Not Not 60 Not Not Not Not Not Not Not 80 30 30 whitening whitened whitened whitened whitened whitened whitened whitened whitened whitened Degree of whitening B A B B Notes to Table 1: *.sup.1 Polylauryllactam; "L1940" of Daicel Chemical Industries, Ltd. *.sup.2 Acrylonitrilebutadiene copolymer rubber; experimental product, bound acrylonitrile = 40 wt %, Mooney viscosity, ML.sub.1 + 4 (100.degree C.) = 52 *.sup.3 Carboxylcontaining acrylonitrilebutadiene copolymer rubber; experimental product, bound acrylonitrile = 40 wt %, carboxyl group content = 2.62 wt % (in monomeric methacrylic acid), Mooney viscosity, ML.sub.1 + 4 (100.degree. C.) = 46 *.sup.4 Epichlorohydrinethylene oxideallyl glycidyl ether copolymer rubber; Zecron 3100 of The Japanese Geon Co., Ltd. *.sup.5 Polyepoxy compound of bisphenol A type; product of YukaShell Co., Ltd. *.sup.6 Overall rubber volume ratio = (V.sub.N + V.sub.E)/(V.sub.N + V.sub.E + V.sub.A) .times. 100; Nitrile rubber volume ratio = V.sub.N /(V.sub.N + V.sub.E) .times. 100; Hydrin rubber volume ratio = V.sub.E /(V.sub.N + V.sub.E) .times. 100; wherein V.sub.N, V.sub.E and V.sub.A represent the volumes of nitrile rubber, hydrin rubber and polyamide resin, respectively, ia a unit blend composition. *.sup.7 at 20 .+-. 3.degree. C. and a drawing speed of 50 mm/min *.sup.8 The sample deteriorated at an ozone concentration of 50 .+-. 5 pphm, elongation of 0-30%, cyclic strain of 60 rpm and temperature of 40 .+-. 2.degree. C. The time when cracking was found to occur by observatio at magnification 10 was designated cracking time. *.sup.9 The sample was drawn at a speed of 50 mm/min (20 .+-. 3.degree. C.), and percent elongation at which the sample turned white was designated percent elongation for whitening. The rating indices for whitening were as follows: A -- The sample whitened only slightly and most of it was transparent. B -- The sample whitened extensively and turned opaque.

A sample material sandwiched between aluminum foils was placed in a mold (210.degree. C.); after preheating for 2 minutes, the material was pressed under a oil press (ca. 100 kg/cm.sup.2) for 10 minutes; the resulting sheet 1 mm thick was removed from the mold, quenched with water and stripped of the aluminum foils. The sheet without aluminum foils was then annealed in vacuum at 150.degree. C. for 1 hour.