Plastic part resistant to deicing salt

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plastic part mainly composed of polyamide resin.
2. Description of the Prior Art
In recent years, many plastic parts have been used in automobiles to reduce their weight and labor for fabrication of their parts. Particularly, 6-nylon and 6,6-nylon are preferably used for plastic parts due to their excellent strengths and thermal resistances. However, it has been found that cracks are likely to occur in plastic parts made of 6-nylon, or 6,6-nylon, or glass fiber reinforced 6-nylon or 6,6-nylon, if they are in contact with calcium chloride included in deicing salts scattered on roads in winter.
SUMMARY OF THE INVENTION
The present invention is completed by studying the problem.
Accordingly, one object of the present invention is to prevent enviromental stress cracking of polyamide parts exposed to calcium chloride included in deicing salts.
The other object of the present invention is to provide a plastic part composed of materials having an excellent strength against stress cracking.
A further object of the present invention is to provide a plastic part that has a durability against calcium chloride in deicing salts.

BRIEF DESCRIPTION OF DRAWINGS
By way of example and to make the description more clear, reference is made to the accompanying drawings in which:
FIG. 1 shows a front view of the radiator of Embodiment 1;
FIG. 2 shows a sectional view of the segmentor case of Embodiment 2;
FIG. 3 shows a sectional view of the canistor case of Embodiment 3;
FIG. 4 shows a front view of the alternationfan of Embodiment 4, and
FIG. 5 shows a front view of the square plate of Embodiment 5, which was taken as a typical example of the plastic parts of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
The inventors of this invention studied this problem and found that such cracks are generated by frequent induction of internal stresses within a plastic part since such part is frequently in contact with calcium chloride included in deicing salts on roads and is subjected to repetitions of heating and cooling. And, the inventors have found that cracking can be prevented by reduction of the saturation water absorbability of polyamide resin used in the above-mentioned plastic parts. The present invention is based on the findings described above.
Description will be made below about the mechanism of the cracking due to calcium chloride in 6-nylon or 6,6-nylon, or glass-fiber reinforced 6-nylon or 6,6-nylon.
In a plastic part, where the outer surface of the part is exposed to ambient air and the inner surface thereof is in contact with water or an aqueous solution, the water absorbed in the outer surface is in equilibrium with ambient air and the inner surface is saturated with water. If the ambient temperature increases or the ambient air becomes dry, the outer surface layer is dried and large tensile strains are induced in the layer, since the inner surface layer remains wet.
It has been found that a significant reduction in elongation to rupture is observed with 6-nylon and 6,6-nylon which have been dried after contact with a concentrated aqueous solution of calcium chloride. The nylons in such condition are similar to the material in the outer surface layer described above.
Thus, cracking will occur in the outer surface layer which is in contact with calcium chloride when the elongation to rupture of the outer layer is exceeded by the tensile strain induced in the same layer.
In such plastic parts, as a radiator tank, a sedimentation tank, or a water valve, there is an outer surface layer which is in contact with ambient air and an internal surface layer which is in contact with water or an aqueous cooling liquid. The former is subject to repetitions of drying and wetting due to ambient humidity and water splashes from roads, while the latter is in a sufficiently wet condition at all times.
When the outer surface layer is dried, large tensile strains are induced on the layer, since the internal layer remains wet. On the other hand, since the outer layer which has been in contact with an aqueous solution having a high concentration of calcium chloride, has a reduced elongation to rupture, the tensile strains exceed the elongation to rupture, leading to crack generation.
Even in plastic parts which are not designed to contain water therein, cracks may occur since the elongation to rupture of the outer layer is reduced owing to contact with an aqueous solution of calcium chloide and tensile strains are induced due to the difference in water contents in the outer and inner layers, in the case when the interior of a plastic part is dewy or in contact with very wet air.
It has been found from the experiment described below that 1.0 mm is the critical thickness of a section of a polyamide part above which cracks are likely to occur.
In an experiment made by the inventors, 6-nylon and 6,6-nylon test pieces with various thicknesses (20 mm.times.20 mm.times.0.5 mm, 20 mm.times.20 mm .times.0.7 mm, 20 mm.times.20 mm.times.1.0 mm, 20 mm.times.20 mm.times.2.0 mm, 20mmx 20 mm.times.3.0 mm) were immersed in a hot water of 100.degree. C. for 40 hrs, and then cooled at room temperature. And, an aqueous solution of 5% by weight calcium chloride was applied on one side of the test pieces. They were dried in an oven of 100.degree. C. for 2 hrs, and cooled at room temperature, followed by water cleaning, and checking for the presence of cracks. According to the experimental results, it was found that cracks were clearly observed in all the test pieces with thicknesses larger than 1.0 mm. In test pieces thinner than 1.0 mm, there was little difference in the dry or wet state between the inner and outer surface layers, which resulted in smaller strains and therefore no cracking. However, cracking occurred in test pieces thicker than 1.0 mm, from the resin described above.
As is easily understood from the above description, the object of the present invention is to prevent environmental stress cracking of polyamide parts exposed to calcium chloride included in deicing salts, by lowering the saturation water absorbability to less than 6.0% in water weight of such polyamide resin as 6-nylon, 6,6-nylon, glass-fiber reinforced 6-nylon, or 6,6-nylon, based on the following reasons;
(1) Tensile strains induced in the outer surface layer can be reduced due to reduced dimensional difference by water absorption between the internal and outer surface layers.
(2) Reduction in the elongation to rupture of the outer surface layer can be suppressed by reducing the amount of calcium chloride impregnating into the resin through the medium of water.
In more detail, the present invention relates to the use of a polyamide resin with a saturation water absorbability less than 6.0%, for plastic parts such as automotive radiator tanks, which contact water on one side of the section and ambient air on another side, have a thickness larger than 1.0 mm and are repeatedly heated above 60.degree. C.
The low water absorbability polyamide resin with a saturation water absorbability less than 6.0% andn including no aromatic ring in the molecule, as described above, includes,
(1) polyamide resins such as 6,10-nylon and 6,12-nylon, which are produced by polycondensation of hexamethylene diamine or a diamine with a methylene group longer than that of hexamethylene diamine and a dicarboxylic acid with a methylene group longer than that of adipic acid, and
(2) polyamide resins such as 11-nylon and 12-nylon, which are produced by ring-opening polymerization of a lactum with a methylene group longer than that of .epsilon.-caprolactum.
The mixture mainly composed of a polyamide resin, with a saturation water absorbability less than 6.0%, which includes modified 6-nylon or modified 6,6-nylon with a saturation water absorbability less than 6.0% by blending 6-nylon and/or 6,6-nylon with one or more than one of the following resins which are mutually soluble with the 6-nylon and/or 6,6-nylon, in more than 30% in by weight, the polyamide resin which is produced by polycondensation of hexamethylene diamine or a diamine with a methylene chain group longer than that of hexamethylene diamine and a dicarboxylic acid with a methylene chain group longer than that of adipic acid, the polyamide resin which is produced by poly condensation of an amino acid with a methylene chain group longer than that of .epsilon.-aminocaproic acid, the polyamide resin which is produced by ring-opening polymeritation of a lactum with a methylene chain group longer than that of .epsilon.-caorolactum, or one of olefinic ionomer resins, such as those with trade names of Surlyn, Himilan, Corporene.
In the present invention, a saturation water absorbability of a resin is expressed as the value of the resin immersed in water of 23.degree. C.
When plastic parts are made of the above mentioned polyamide resins or a mixture including a polyamide resin as the main component, the parts exhibit high strength and high heat resistance, and are highly resistant to deicing salts.
In addition, as long as the properties of the above described polyamide resins are not significantly varied, the polyamide resins or the polyamide-based mixtures may include reinforcing materials such as glass fibers, pigments, age resistant additives and extenders.
The plastic parts or components relevant to the present invention, which have a vessel-like, hose-like, or other shape with the section which is in contact with water inwardly and that in contact with ambient air outwardly, and are subjected to repetitive heating above 60.degree. C., include automotive radiator tanks, sedimentation tanks for diesel injection pumps, and water valves in automobiles.
And, the plastic parts which have a vessel-like, hose-like, or other shape with a section thicker than 1.0 mm and are subjected to repetitive heating above 60.degree. C., include casings of canisters for adsorbing evaporated fuel, and fans of alternators used as generators, in automobiles.
The above-described radiator tank, which contains water for engine cooling, keeps warm water therein and is repeatedly heated by the heat from the cooling water.
The sedimentation casing, used for separating water from light oil and retaining the water, is repeatedly heated by the heat accumulated in an engine room or compartment.
The water valve used for transferring engine cooling water to a room heating equipment retains warm water and is repeatedly heated by the heat from the cooling water.
The canister casing containing active carbon for adsorbing gasoline vapor has a section thicker than 1 mm and is heated by heat of adsorption and heat accumulated in an engine room.
And, the alternator fans used for cooling an automotive alternator generating alternating current has a section thicker than 1 mm and is heated by the heat accumulated in an engine room.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described in detail by way of preferred embodiments.
Embodiment 1
Plastic parts of the present embodiment are employed in upper tank 1 and lower tank 2 of an automobile radiator, which are shown in FIG. 1. As the polyamide resins, various glass fiber reinforced thermoplastic resins shown in Table 1 were used, and said tanks were injection-molded therefrom. The molded products from No. 1 to No. 8 in Table 1 are the plastic parts resistant to deicing salt according to the present invention, while the molded products from No. 101 to No. 103 are the conventional ones.
As the tests for evaluating the resistance of the plastic parts against deicing salt, the following methods A, B and C were used;
Test method A
Several radiators provided with said plastic tanks made from corresponding each of the polyamide resins are offered as the test pieces. As a pre-treatment, each of the radiators was immersed into hot water of 80.degree. C. for 20 hrs than taken out, and a common cooling liquid for radiator was filled in and closed tightly, then put in an oven at 100.degree. C. and kept for 24 hrs for drying, the outer surfaces of the tanks of the radiator was taken out of the oven and cooled. Next, each of the radiators was subjected to a cycle test, that is 5% calcium chloride aqueous solution was coated on the outer surfaces of each of the preteated plastic tank. Then, each of the radiators was kept in an atmosphere of 100.degree. C. for 2 hrs, for drying the aqueous solution coated, further after leaving it in an atmosphere of room temperature for 1 hr, washed with water. In this case, a series of the above processings consists of one cycle of the cycle test.
Practically, the repeated cycle tests were carried out with 10, 20, 40 and partially 100 cycles. After testing, each of the tested tanks was checked by means of a "penetration test" with regards to the crack. Each of the cracked parts found were cut off, and the depth of each of the cracks, which was defined as a straight distance from the surface to the bottom end of the crack, was measured by means of a microscope.
Test method B
The testing procedures are the same as the method A except the calcium chloride aqueous solution. The calcium chloride solution of the test method of B is of a concentration of 40% (weight %).
Test method C
The testing procedures are the same as the method B, but the pre-treatments were not carried out.
In Table 1 are shown the saturation water absorptivities (saturation water absorptivity in water of 23.degree. C.) and the measured crack depths. Also in Table 1, the symbol shows 6,12-nylon, E; 6,10-nylon, F; a blend of 6,6-nylon and 6,12-nylon having a blending ratio of 1/1, G; a blend of 6,6-nylon and 6,10-nylon and having a blending ratio of 1/1, H; a blend of 6,6-nylon and 6,12-nylon having a blending ratio of 1/1, I; a blend of 6,6-nylon and Olefinic Ionomer having ratio of 7/3, J; a blend of 6,6-nylon and Olefinic Ionomer having a blending ratio of 6/4, Y; 6,6-nylon and Z; 6-nylon respectively.
As clear from Table 1, the tanks of No. 101 to 103 made from conventional 6,6-nylon or 6-nylon had cracks of 1.6 to 2.2 mm deep after the test of 10 cycle, while the tanks of No. 1 to 8 according to the present invention had cracks of 0.0 to 1.2 mm deep even after the test of 40 cycle. The growing speed of cracks of the tanks of the present invention was quite slow. Especially, on the tanks made from 6,12-nylon or the blend of 6-nylon and Olefinic Ionomer having a blending ratio of 6/4 there were never observed any cracks at all.
Embodiment 2
As the plastic part of the present embodiment is employed a segmentor (Water-separator) case 3 for Diesel injection pump shown in FIG. 2.
Thermo-plastic resins shown in Table 2, were used and injection molded to produce the segmentor case. The symbols in the table, G, J, D, F, and Z show the practice of the same symbols in Table 1, furthermore, K shows a blend of 6-nylon and Olefinic Ionomer =3/7.
The molded products of Nos. 9 to 13 in Table 2 are the plastic parts according to the present invention, while No. 104 is a conventional plastic part.
As for the test for evaluating the resistance of the plastic parts, a number of the segmentors were offered which were provided with each of the cases molded from the corresponding plastics. At first, each segmentor was submitted to a pre-treatment, that is, it was immersed into hot water of 80.degree. C. for 24 hrs, taken out and after being filled with water, was left in an atmosphere of 100.degree. C. for 20 hrs. Thus, after the pretreatment, each of the segmentors was submitted to the cycle tests, wherein each segmentor was coated on the outer surface thereof with 5% calcium chloride aqueous solution, then left in an atmosphere of 100.degree. C. for 2 hrs, and after leaving it at the room temperature for 1 hr, washed with water. One series of such processing was taken as one cycle, and such cycle or cycles were applied to each of the segmentors.
Practically, several segmentors of each No. were tested at the same time. Each one of the segmentors was taken out after the corresponding cycle or cycles of 1,5,10 and 20, respectively. Each of the cracks of the tested segmentors were checked by means of a "penetration test", and each of the cracked parts was cut off and the crack-depths were measured by means of a microscope.
The results obtained are shown in Table 2. For the plastic parts made from the conventional 6-nylon (No. 104), cracks of 3.0 mm deep were produced after 5 cycles, while the segmentor cases according to the present invention, as shown as No. 9 to 13, had the cracks of only 0 to 0.8 mm deep even after 20 cycle testing. The crack growing of the plastic parts of the present invention was remarkably slow. Especially, in the segmentor cases made from 6,12-nylon, a blend of 6,6-nylon/6,12-nylon=1/1, a blend of 6,6-nylon/Olefinic Ionomer=1/1, there were never found any cracks at all.
Embodiment 3
This embodiment relates to a canistor case 4 shown in FIG. 3. Several kinds of the canistor cases were made from the thermo-plastics resins shown in Table 3, by injection-molding.
The symbols in Table 3, D, G, J, and Y correspond to the symbolical expression D, G, J and Y in Table 1.
The molded products, Nos. 14 to 16 in Table 3 are all the plastic parts according to the present invention, While Nos. 105 and 106 are both the conventional plastic parts. As the pre-treatment, at first, the plastic parts being absolutely dried condition were put in a constant temperature-humidity bath, the atmosphere of which had a temperature of 80.degree. C. and a relative humidity of 95%. The plastic parts were kept for 33 hrs, then taken out, and left at the room temperature for 12 hrs. Next, the parts were submitted to the cycle tests wherein each pre-treated plastic part was coated on the surface thereof with 5% calcium chloride aqueous solution, left in an atmosphere of 100 .degree. C. for 2 hrs, then left at the room temperature for 1 hr, and washed with water. One series of such processing was taken as one cycle, and such cycle or cycles were applied to the plastic parts.
Practically, several plastic parts were tested at the same time. And each one of the plastic parts was taken out after the corresponding cycle or cycles of 1,10 and 20 respectively. And the cracks thereof were checked by means of "penetration test", then each cracked part was cut off, and the crack-depth was measured by means of a microscope.
Results obtained are shown in Table 3. For the plastic parts made from the conventional 6,6-nylon, regardless of whether they contain glass fibers or not, had the cracks of 1.7 to 1.8 mm deep at 10 testing cycles, while for the canistor cases according to the present invention, there were never found any cracks at all, even at 20 testing cycles.
Embodiment 4
This embodiment is an alternator fan composed of a base 5 and blades 6, as shown in FIG. 4.
As the resin forming the base 5 and brades 6 of the alternator, thermoplastic resins shown in Table 4 were used, and injection molded. The symbols F and Y in Table 4 show the same thermoplastic resins as those shown in Table 1.
A plastic part of No. 17 in Table 4 is a plastic part according to the present invention, while a plastic part of No. 107 is a conventional plastic part. As for the test for evaluating the resistance of the plastic parts, the test employed in Embodiment 3 was carried out in this Embodiment.
The obtained test results are shown together in Table 4. The plastic part of No. 107 which was made from conventional 6,6-nylon had cracks of 1.9 mm deep after 20 testing cycles, while in the alternator fan No. 17 of the present invention cracks were never found at all, even after 20 testing cycles.
Embodiment 5
As for this embodiment, there are supposed various possible plastic parts, and 20 mm.times.20 mm.times.3 mm square plate 7 shown in a FIG. 7 was taken as a typical example of the plastic parts of the present invention.
As polyamide resins, the thermoplastic resins shown in Table 5 were employed. The symbols D, E, F, G, H, I and J in Table 5 show the same resin as the corresponding symbols in Table 1 respectively. The symbols L, M, N, O and P show a blend of 6,6-nylon/6,12-nylon=3/7, a blend of 6,6-nylon/11-nylon=1/1, a blend of 6-nylon/Olefinic Ionomer=1/1 and nylon MXD6 having arpsomatic ring in molecular chains respectively. Nos. 18 to 36 in Table 5 are all the plastic parts according to the present invention, while Nos. 108 to 112 are the conventional plastic parts. No. 201 is an example for comparision. As for the test, after the square plates (20mm.times.20 mm.times.3 mm) were boiled in water of 100.degree. C. for 40 hrs, cooled at the room temperature. Then the plates were subjected to the cycle tests. At first 5% calcium chloride square solution was coated on one of the front and back surfaces of each said plate, dried in a 100.degree. C. oven for 2 hrs, after cooled at the room temperature, washed with water, and the series of the aforementioned processing was taken as the first cycle. Then, the plates were boiled in water aqueous solution is wholly coated on the same surface as in the first cycle, dried up in an 100.degree. C. oven for 2 hrs after cooled, washed with water, this series of the above processings was taken as the second cycle. Hereafter, if necessary, the same cycle as the second cycle was repeatedly applied to the plates. Practically several plates of each No. were tested together at 1, 5, 10, 20 and 40 cycles, respectively, and one of the corresponding plates was taken out at the corresponding cycle test, and the cracks thereof were checked by means of a "penetration test", each cracked part was cut off, and the cracked-depth was measured by means of a microscope.
Results obtained are shown together in Table 5. When the conventional 6-nylon, 6,6-nylon are used for the plates, the plates which did not include glass fibers had a crack of 2.5 mm deep at one cycle, while the plates including said fibers had cracks of 1.4 to 1.6 mm deep at 40 cycles.
In contrast, the plates according to the present invention had cracks of only 0 to 0.3 mm deep even at 40 cycles, and an slow crack growth was found, especially for the plate made from 6,12-nylon and the blend of 6,6-nylon/Olefinic Ionomer=6/4, the appearance of cracks was not observed at all. However, the plate made from Nylon MXD6 for comparison, had a crack of 3.0 mm deep at 20 cycles, and it is obvious that the crack growth is more remarkable than in the conventional 6-nylon and 6,6-nylon.
TABLE 1__________________________________________________________________________Materials Crack depth afterResin Glass fiber testing at givenWater contents Testing cycle of cycles (mm)Sample No. Absorpability (%) Method 10 20 40 100 Remarks__________________________________________________________________________1 D (wt %) A 0.0 0.0 0.0 0.0 (3) 33 B 0.0 0.0 0.0 0.0 C 0.0 0.0 0.0 0.02 E 33 A 0.0 0.1 0.3 -- (4) B 0.3 0.5 0.7 -- C 0.3 0.3 0.7 --3 F 33 A 0.0 0.0 0.0 -- (5.5) B 0.1 0.2 0.5 -- C 0.0 0.2 0.4 --4 G 45 A 0.2 0.2 0.4 -- (6) B 0.3 0.6 0.0 -- C 0.3 0.4 0.7 --5 H 45 A 0.2 0.3 0.6 -- (4.7) B 0.3 0.5 0.7 -- C 0.3 0.4 0.7 --6 I 33 A 0.3 0.4 0.8 -- (5.6) B 0.5 0.7 1.2 -- C 0.4 0.6 1.2 --7 J 33 A 0.0 0.0 0.0 -- (4.8) B 0.0 0.0 0.0 -- C 0.0 0.0 0.0 --8 J 45 A 0.0 0.0 0.0 -- (4.8) B 0.0 0.0 0.0 -- C 0.0 0.0 0.0 --101 Y 30 A 1.6 2.0 2.2 -- Perforated (8) B 2.2 2.3 2.4 -- at 90 cycles C 2.0 2.2 2.5 --102 Y 45 A 1.9 2.0 2.2 -- Perforated (8) B 2.2 2.3 2.5 -- at 90 cycles C 2.7 2.3 2.4 --103 Z 30 A 2.0 2.2 2.6 -- (10.7) B 2.2 2.4 2.7 -- C 2.1 2.2 2.7 --__________________________________________________________________________
TABLE 2______________________________________Materials Crack depth after Resin Glass fiber testing at givenSample Water contents cycle or cycles (mm)No. Absorpability (%) 1 5 10 20 Remarks______________________________________ 9 G (6) 0 0.0 0.2 0.3 0.810 K (3.2) 0 0.0 0.0 0.0 0.011 J (4.8) 0 0.0 0.0 0.0 0.012 D (3) 0 0.0 0.0 0.0 0.013 F (5.5) 0 0.0 0.0 0.0 0.0104 Z (10.7) 0 1.5 3.0 -- --______________________________________
TABLE 3______________________________________Materials Crack depth after Resin Glass fiber testing at given Water contents cycle or cycles (mm)Sample No. Absorpability (%) 1 10 20 Remarks______________________________________ 14 D (3) 0 0.0 0.0 0.0 15 G (6) 0 0.0 0.0 0.0 16 J (4.8) 0 0.0 0.0 0.0105 Y (8) 0 0.9 1.8 -- perforated at 12 cycles106 Y (8) 30 0.2 1.7 --______________________________________
TABLE 4______________________________________Materials Crack depth after Resin Glass fiber testing at given Water contents cycle or cycles (mm)Sample No. Absorpability (%) 1 10 20______________________________________ 17 F (5.5) 45 0.2 1.6 1.9107 Y (8) 43 0.0 0.0 0.0______________________________________
TABLE 5______________________________________ Materials Crack depth after Resin Glass fiber testing at given Water contents cycle or cycles (mm)Sample No. Absorpability (%) 1 5 10 20 40______________________________________18 D (3) 0 0.0 0.0 0.0 0.0 0.019 D (3) 33 0.0 0.0 0.0 0.0 0.020 D (3) 43 0.0 0.0 0.0 0.0 0.021 E (4) 33 0.0 0.0 0.0 0.0 0.022 F (5.5) 0 0.0 -- -- -- --23 F (5.5) 33 0.0 0.0 0.0 0.2 0.224 L (4.5) 33 0.0 0.0 0.0 0.0 0.025 G (6) 0 0.1 -- -- -- --26 G (6) 33 0.1 0.1 0.1 0.2 0.227 H (4.7) 45 0.1 0.1 0.2 0.2 0.328 M (4.9) 45 0.1 0.1 0.2 0.3 0.329 I (5.6) 0 0.0 -- -- -- --30 I (5.6) 33 0.0 0.1 0.1 0.2 0.331 J (4.8) 0 0.0 -- -- -- --32 J (4.8) 33 0.0 0.0 0.0 0.0 0.033 N (5.3) 0 0.1 -- -- -- --34 N (5.3) 30 0.1 0.1 0.1 0.2 0.335 O (5.4) 0 0.0 -- -- -- --36 O (5.4) 30 0.0 0.2 0.2 0.3 0.3108 Y (8) 0 2.5 -- -- -- --109 Y (8) 30 0.2 0.4 0.7 1.2 1.5110 Y (8) 45 0.2 0.5 0.6 1.2 1.4111 Z (10.7) 0 2.8 -- -- -- --112 Z (10.7) 30 0.4 0.9 1.1 1.4 1.6201 P (5.8) 30 0.4 0.9 1.3 3.0 3.0______________________________________

Number	Name	Date	Kind
4465821	Nieglinger	Aug 1984
4482695	Barbee et al.	Nov 1984

Plastic part resistant to deicing salt

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