JPH08189416A - High-rigidity resin cover - Google Patents

Abstract

PURPOSE: To provide a high stiffness resin cover used in an internal combustion engine for automobiles and drive systems. CONSTITUTION: This resin cover contains 60 wt.pts in total by adding glass fiber and mineral filler to 40 wt.pts of polymide resin, and its distribution consists of 35 to 55 wt.pts of glass fiber and 5 to 25 wt.pts of mineral filler. It is constituted of a polyamide resin component having melting resin viscosity at molding in the range of 50 to 200 pascal seconds under shearing velocity of 1,216 sec<-1> .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a highly rigid resin cover,
In particular, the present invention relates to covers used for internal combustion engines and drive systems for automobiles. More specifically, a cover material used for internal combustion engines and drive systems is molded and configured by using a reinforced resin material containing glass fiber and mineral filler. The present invention relates to a high-rigidity resin cover.

[0002]

2. Description of the Related Art The following types of covers are used as covers for conventional internal combustion engines for automobiles. Resin covers made of linear polyamide polymer (nylon 66) with 10% glass fiber and 30% inorganic fiber reinforced. Aluminum alloy cast covers and the like are used.

[0003]

However, in the case of such a conventional automobile internal combustion engine cover, in the case of the resin cover of (a), the cover which is a molded product is thermally deformed in a high temperature atmosphere. Oil leakage may occur, and (b) the molded product may warp or deform even at room temperature. Therefore, (c) In order to avoid the problems of (a) and (b) above, if the mounting surface flange shape is made thick and the number of mounting bolts is increased, the cover cost will increase and the weight will increase. Will cause Further, (d) due to the change or deformation of the elastic modulus and strength at high temperature, a heavy object such as a plug ignition coil cannot be mounted on the upper surface of the rocker cover or the like.

Further, in the case of a resin cover, in order to improve the mechanical strength of the molded product, for example, rigidity and strength,
It is necessary to increase the mixing ratio of glass fiber with respect to the amount of polyamide resin. However, in the conventional glass fiber reinforced polyamide resin composition, if the proportion of glass fiber is increased, the flow of the resin composition during molding, particularly during injection molding becomes poor, and it becomes difficult to mold large parts or parts having a rib structure. There was a problem.

Further, when the mixing ratio of glass fiber in the polyamide resin is increased, there is a problem that the glass fiber floats on the surface of the molded product and impairs the surface appearance of the molded product.

Next, regarding the above-mentioned cover, (a) the cost is high, (b) the weight is heavy, (c) the noise is deteriorated due to the increase of solid transmission, etc. As mentioned above, there are various problems.

An object of the present invention is to solve such conventional problems and to provide a high-rigidity resin cover having excellent performance particularly as a cover for an internal combustion engine for automobiles.

[0008]

Means for Solving the Problems The present inventors formed a cover for an automobile internal combustion engine by using various resin materials in order to achieve the above object and compared the performances. As a result, a linear polyamide-based polymer was obtained. In addition, they have found that a cover formed by using a resin material reinforced by mixing a specific amount of glass fiber and a mineral filler has an excellent performance of high rigidity, and has accomplished the present invention.

That is, the high-rigidity cover of the present invention contains 60 parts by weight of glass resin and mineral filler in 40 parts by weight of polyamide resin, and the distribution is 35-55 parts by weight of glass fiber and 5-mineral filler. It is characterized in that it is composed of a polyamide resin composition of 25 parts by weight, and the viscosity of the molten resin at the time of molding is in the range of 50 to 200 Pascal seconds under the shear rate of 1216 sec ^-1 .

The present invention will be described in detail below. In order to improve the moldability of the polyamide resin composition, it is necessary to increase the fluidity of the polyamide resin composition. Generally, lowering the molecular weight of polyamide increases the fluidity of polyamide,
If a low molecular weight polyamide is used, the mechanical properties of the molded product will deteriorate, and the flowability of the polyamide resin composition filled with a reinforcing material will vary depending on the type of reinforcing material, so it is not always optimal to just specify the molecular weight of the polyamide. Liquidity cannot be obtained. There is also a method of reducing the compounding amount of the reinforcing material in order to improve the moldability, but this reduces the strength of the molded product. Further, when the compounding amount of the reinforcing material is increased, the surface appearance of the molded product is impaired.

In the present invention, in order to achieve a good balance between the moldability of the polyamide resin composition, the strength of the molded article and the appearance thereof, the criteria to be defined are the mixing ratio of the polyamide resin and the reinforcing material, and the polyamide resin composition. It was found that it was two of the viscosity of the molten resin under the shear rate of 1216 sec ^-1 , and limited these specific ranges, and further it was excellent by adopting glass fiber and mineral filler as the reinforcing material. It achieves moldability, high strength of the molded product, favorable surface appearance and low warpage at the same time.

In the present invention, the molten resin viscosity at the time of molding of the polyamide resin composition means the molded article obtained by molding the polyamide resin composition, the resin temperature at the time of absolute drying, the molding speed and the shear rate of 1216 sec. ^{It means} the viscosity when measured under the condition of ^-1 . This viscosity can be measured using, for example, a KAYNESS capillary viscometer. The resin temperature during molding is, for example, about 280 ° C. in the case of a composition using nylon 66 as the polyamide resin.

When the viscosity of the molten resin during molding of the polyamide resin composition is less than 50 Pascal seconds under a shear rate of 1216 sec ^-1 , burr occurs during molding because of the low viscosity of the resin composition. Also, there is a problem in moldability such as dripping of the resin composition from the nozzle of the molding machine (so-called dripping phenomenon), which is not preferable. On the other hand, when the viscosity of the molten resin at the time of molding becomes more than 200 Pascal seconds, in the resin composition in which 50% by weight or more of the mineral filler and the glass fiber are filled like the composition used in the present invention, the mineral filler, etc. In addition to the appearance of defects such as poor appearance due to the reinforcing material of item (1) emerging on the surface of the molded product, and a high injection pressure is required because the resin composition is likely to be unfilled in the thin portion during injection molding, which is not preferable.

The polyamide resin composition used in the present invention is
In particular, the resin temperature during injection molding (usually 15 ° C
It is preferable that the viscosity of the molten resin at a temperature of 40 ° C. higher) is adjusted to 50 to 200 Pascal seconds under a shear rate of 1216 sec ⁻¹ , and molding is performed by an injection molding method.

The polyamide resin composition used in the present invention is
It is a combination of a matrix polyamide resin and glass fiber, which is a normal reinforcing material, and a mineral filler. The blending amount of these reinforcing materials is selected according to the physical properties such as rigidity and strength of the molded product, and the degree of warpage allowed for the molded product. Although it depends on the kind of the mineral filler, generally, the larger the amount of the mineral filler filled, the more accurate a molded product with less warp can be obtained, and at the same time, the matte type having a surface appearance is preferable. On the other hand, the rigidity, strength, etc. tend to be lower than when the glass fiber alone is filled in the same amount. Therefore, the polyamide resin composition used in the present invention gives a molded article having required physical properties and low warpage and excellent surface appearance by adjusting the type of mineral filler and the mixing ratio thereof with glass fiber. It is possible.

In the present invention, the weight of the reinforcing material to be blended with the polyamide resin, that is, the glass fiber and the mineral filler, is based on the total weight of the polyamide resin and the reinforcing material, specifically, the weight of the polyamide resin and the reinforcing material. Expressed in parts by weight when the total weight is 100 parts by weight, 60 parts by weight of glass fiber and mineral filler are used as the reinforcing material, and the distribution is 35 to 55 parts by weight of glass fiber and 5 to 25 parts by weight of mineral (inorganic) filler. Is mixed with 40 parts by weight of a complementary amount of polyamide resin. When the content of the reinforcing material is more than 60 parts by weight of the specified range, the moldability such as fluidity and processability of the resin composition is deteriorated, and at the same time, it becomes difficult to obtain a uniform mixed dispersion state. The condition also gets worse. If the compounding amount of the reinforcing material is less than this specified range, the mechanical strength of the molded product will be insufficient. The distribution of the glass fiber and the mineral filler of the reinforcing material is because the warpage of the molded product is small and the high rigidity is obtained within the above range, and 45 parts by weight of the glass fiber and 15 parts by weight of the mineral filler are the optimum blending.

The polyamide resin used as the matrix in the present invention preferably has a low viscosity. Specifically, those having a low viscosity such that the melt viscosity at 1216 sec ^-1 at the temperature of the injection molding resin (15 ° C. to 40 ° C. higher than the melting point) at the time of absolute drying is particularly 80 Pascal seconds or less are preferable. Such a low-viscosity polyamide resin is a low-molecular weight polyamide by controlling the molecular weight during the polymerization, for example, by controlling the water content during the polymerization,
Alternatively, it can be obtained by mixing a high molecular weight polyamide and a low molecular weight polyamide. The mixing in this case may be mixing in the form of pellets or mixing in the molten state during kneading. When the melt viscosity of the polyamide resin is lowered, it wets the surface of the glass fiber or the like mixed with the polyamide resin, so that the processability and moldability of the polyamide resin composition are improved, and the filled glass fiber or the like is the surface of the molded product. It is also prevented from protruding.

The polyamide used in the present invention is a polymer having an amide bond in the main chain, which is a linear synthesis obtained by polymerizing a diamine and a dibasic acid, ring-opening polymerization of lactam, and polycondensation of aminocarboxylic acid. The polymer is, for example, nylon 6, nylon 66, nylon 68, 610, 612, or the like, or a copolymerized nylon thereof, including aromatic polyamide.

In the present invention, as the glass fiber, glass fiber usually used as a reinforcing material can be used. That is, long-fiber or short-fiber glass having any shape can be used. Depending on these glass fiber lengths, when compounding with an extruder, the screw design is taken into consideration, or a downstream system or the like is adopted. Preferably, chopped strand type short fiber glass, for example, commercially available chopped strand glass short fiber having a diameter of 10 microns and a length of 3 mm is used.

In the present invention, the mineral filler is, for example, SiO ₂ —MgO type talc, SiO ₂ —CaO type wollastonite (calcium silicate), SiO ₂ —Al ₂ O ₃ type kaolin, SiO. _2- Al ₂ O ₃ -K ₂ O based mica, calcium carbonate, calcium sulfate, aluminum hydroxide, magnesium oxide and the like can be mentioned. As these mineral fillers, talc, wollastonite, kaolin, mica and the like having a particle size of 0.3 to 20 μm, whose surface is treated with aminosilane, are preferable.

The polyamide resin composition used in the present invention is
In addition to the above polyamide resin, glass fiber and mineral filler, one or more additives, such as oxidation,
For the purpose of stabilizers and inhibitors against heat and UV deterioration, lubricants and release agents, colorants including dyes and pigments, nucleating agents, foaming agents, plasticizers, inorganic fillers, flame retardants and antistatic agents. It can be added as appropriate.

The cover of the present invention can be formed by molding the above polyamide resin composition, preferably by injection molding. For example, a car rocker cover is a rocker cover main body that integrally includes a mounting flange, a fastening bolt seat, a blow-by separator chamber, an oil inlet, a blow-by pipe, and a baffle plate mounting flange, and is integrally molded with the above polyamide resin material. A material having a linear expansion coefficient close to that of the main body material, such as glass fiber
(GF) 10% by weight and mineral filler (MF) 30% by weight Nylon 66 is mixed to form a baffle plate that is integrally molded with a partition plate and a flat surface. can do.

[0023]

Next, the operation will be described. The resin cover of the present invention is
Conventional resin material (linear polyamide polymer (nylon 6
6) + glass fiber 10% by weight + inorganic fiber 30% by weight) compared to 35 to 55 parts by weight of glass fiber and 5 to 25 parts by weight of mineral filler, (1) elasticity at room temperature and high temperature. Rate, tensile strength, and other physical properties are about 2-3 times higher, and the rate of change with temperature is small, so the mounting flange, bolt seat, and general wall thickness can be reduced, and cost and weight can be reduced. Is possible. At the same time, since heavy objects such as plug ignition coils, which were not possible with conventional resin materials, can be mounted on this cover,
The engine can be made compact. Furthermore, (2) the viscoelastic property of the main body material is the same as that of conventional materials, so it has high vibration damping performance, which is a characteristic of resin materials.By using this as a rocker cover, high quietness can be realized. . (3) In the present invention, since the reinforcing material with different distribution is used compared to the conventional one, the thermal deformation and warpage characteristics of the main body material that is the cover are about 1/2 or less compared to the conventional material. Therefore, the gasket seal flange can be made thinner,
In addition, since the number of cover mounting bolts can be reduced, cost and weight can be reduced.

[0024]

[Test Examples] The present invention will be specifically described below with reference to test examples. Test Example 1 (Preparation and Evaluation Method of Samples Containing Mineral Filler and Mineral Filler and Glass Fiber) Nylon 66 or a blend of Nylon 66 and 6 was commercially available as glass fiber with a diameter of 10 μm and a chopped strand glass short length of 3 mm. Fiber with a properly designed screw,
For example, it was melt-kneaded by using a twin screw extruder having a screw diameter of 40 mm manufactured by W & P Corporation. At this time, the extruder barrel temperature and the screw rotation were adjusted so that the molten resin temperature was 280 ° C to 300 ° C. Similarly, silane-treated kaolin clay as a mineral filler was melt-kneaded with nylon 66 or a blend of nylon 66 and 6. The obtained two kinds of kneaded products were mixed so that the compounding ratio of the mineral filler and the glass fiber as shown in Table 1 was obtained,
The resin pellets of Sample Nos. 1 to 7 were used. Sample N
o.8 is a commercial product ZYTEL (nylon 66 62 manufactured by DuPont)
Parts by weight, glass fibers 10 parts by weight, mineral filler 28 parts by weight). Sample Nos. 1 to 4 use the polyamide resin composition according to the present invention, and Sample Nos. 5 to 7 are for comparison. Each of the resin pellets thus obtained was injection-molded as described below to obtain the molded products of Sample Nos. 1 to 8, the moldability evaluation, the warpage and surface condition of the molded products, and the mechanical properties thereof. It was measured. Each resin pellet was previously dried with dry air at 80 ° C. prior to molding.

For the evaluation of moldability, each resin pellet was 45 cm
Injection-molded into a box-shaped part measuring 19 cm × 8 cm, and comprehensively evaluated the pressure required for the molding, the ease with which the mold can be filled, the barrel of the molding machine, and the state of nasal sagging at the nozzle. Good,
It was expressed in four stages of good and bad. In addition, the surface condition such as the surface roughness of the molded product and the warpage of the molded product were visually evaluated.

For the sled of a large plate-shaped molded article,
No. 1 and sample No. 5 pellets, length 400 mm x width
Injection molding was performed on a plate having a rib structure of 100 mm × 10 mm in thickness, and the amount of warpage was measured 24 hours after the molding, and the warpage state is shown in FIGS. 1 (a) and 1 (b). For these resin pellets, in order to check the correlation with the amount of warpage, 76 mm (3 in)
A × 127 mm (5 in) × 3 mm (1/8 in) plate was molded and the molding shrinkage was also measured.

To measure the physical properties of molded parts, each resin pellet was measured on a 6 oz injection molding machine according to ASTM D 638 1
It was molded into a 3 mm × 130 mm × 3.2 mm test piece. The holding time was 5 to 6 minutes, the barrel temperature was 270 to 280 ° C, and the nozzle temperature was 280 to 290 ° C. The mold temperature was about 90 ° C. and a fast molding cycle of 10/20 or 20/20 molding cycles (second of ram advance / second of hold) was performed. With respect to the obtained molded article for physical property test, various physical property values were measured immediately after molding and at 150 ° C.

The molten resin viscosity of the above-mentioned molded product (size) was measured by using a Capillograph viscometer manufactured by Toyo Seiki Co., Ltd. when the molded product was absolutely dried (containing 0.1 to 0.15% of water), 28
The melt viscosity was measured at 0 ° C. and a shear rate of 1216 sec ⁻¹ .

The measurement results are shown in Table 1 below.

[Table 1]

The following can be understood from the results of the above sample Nos. 1 to 8. First, regarding the effect of the mineral filler and the combination of the mineral filler and the glass fiber, the sample No. 1 containing the mineral filler and the glass fiber was used.
The flexural modulus, flexural strength, and tensile strength of No. 4 are significantly higher than those of No. 8 which is a commercially available material manufactured by DuPont, and the material obtained by the present invention has high rigidity,
It has been shown to be suitable for many applications requiring strength. Further, from the comparison between Sample No. 8 and Sample Nos. 1 to 4, glass fiber alone has high rigidity and strength, but leaves room for further improvement in moldability, surface appearance of molded products and warpage of molded products made of glass. It can be seen that this can be improved by using a mineral filler in combination with the fiber. High rigidity,
The combination of strength, good moldability, surface appearance, and degree of warpage is brought about by the high viscosity of the mineral filler and glass fibers, as well as the melt viscosity of the polyamide resin composition. In sample No. 6 having a high melt viscosity exceeding the range of the present invention, the resin filling was likely to be insufficient under normal injection molding conditions, and the surface appearance of the molded product was extremely poor. Further, in sample No. 7, the resin viscosity was too low and the resin dripped severely on the nose, and molding was difficult.

As shown in FIG. 1, the amount of warpage of a plate having a rib structure of 400 mm × 100 mm × 10 mm, as shown in FIG. 1, is a sample containing 15% and 45% of mineral filler and glass fiber, respectively.
The molded product of No. 1 is sample No. 5 containing only 60% of glass fiber.
It shows a smaller warpage compared to the molded product of No. 1
It is shown that the molded product of (1) is a material that balances high physical properties and low warpage.

Finally, regarding the relationship between the compounding amount of the reinforcing material and the melt viscosity of the polyamide resin composition, a sample of 38% of the reinforcing material was used.
The molded products of No. 8 and 60% reinforced sample No. 5 use the same nylon 66, but the sample No. 8 has good moldability, but the reinforced sample increased. In No. 6, the viscosity is too high. From this, it is understood that adjusting the melt viscosity of the polyamide resin composition is important because the flow becomes worse if the reinforcing material is simply increased.

Test Example 2 Using the same glass fiber (GF) as used in Test Example 1 and silane-treated kaolin clay as a mineral filler (MF), resin pellets obtained by compounding and strengthening nylon 66 with the following compounding amounts were used. Flat plate T / P (250mm x 100mm x 3mm) was injection-molded to obtain sample Nos. 9 to 11 flatness immediately after molding (initial stage) and after aging for 500 hours at 150 ° C ambient temperature. Was measured using a three-dimensional measuring machine. Table 2 shows the maximum deformation amount data. Sample No. 9: 30 parts by weight of glass fiber, 30 mineral fillers
Parts by weight (represented by GF30MF30) Sample No. 10: 45 parts by weight of glass fiber, 15 mineral fillers
Parts by weight (GF45MF15) Sample No. 11: Glass fiber 60 parts by weight (GF60) Sample No. 12: DuPont commercial product ZYTEL (glass fiber)
10 parts by weight, 28 parts by weight of mineral filler, GF10MF28) Fig. 2 shows the relationship between the GF amount and the MF amount of the molded products of sample Nos. 9 to 12 (immediately after molding) and the warpage.

[0034]

[Table 2]

Next, sample Nos. 9 to 12 were heated at 23 ° C. and 150 ° C.
The flexural modulus at ℃ and 200 ℃ was measured. Measurement is ASTM
Compliant with D 790. The obtained results are shown in Table 3, and the relationship between the GF amount, the MF amount and the flexural modulus (23 ° C) is shown in Fig. 3.

[0036]

[Table 3]

Further, for sample Nos. 9 to 12, flexural modulus (conforming to ASTM D 790) and flexural strength (conforming to ASTM D 790).
And tensile strength (according to ASTM D638) were measured, and the obtained results are shown in Table 4, Table 5 and Table 6, respectively.

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

Next, with respect to Sample No. 10 and Sample No. 12, the dynamic viscoelasticity was measured by the following measuring method. Test piece shape: 1 mm x 2 mm x 60 mm Test mode: pulling The test piece was vibrated at 110 Hz in a constant temperature bath, and the value of tan δ at each temperature shown in Table 7 was measured. The results obtained are shown in Table 7. In the dynamic viscoelasticity measurement, the storage elastic modulus (E ′) that represents elastic properties, the loss elastic modulus (E ″) that represents viscous properties, and the ratio of loss elastic modulus to storage elastic modulus are t
Can measure anδ. When evaluating the sound vibration characteristics, the value of tanδ, which indicates the ratio of damping effect to input, is emphasized.
In other words, the material with larger tan δ value has better sound and vibration performance.

[0042]

[Table 7]

As shown in the above table, in the atmospheric temperature range in the automobile engine room, the molded product of No. 10 using the polyamide resin composition according to the present invention is better than the molded product of No. 12 on the market. Also, the value of tan δ is large and the sound vibration effect is excellent.

Next, FIG. 4 shows the deformation amount (flange floating amount) and the span between bolt spans due to the gasket reaction force of the flange at high temperature when the rocker covers of sample No. 10 and sample No. 12 were molded. showed that. For example, if the flange deformation is designed to be about 0.2 mm, the bolt span distance can be designed to be about 130 mm for the molded product of sample No. 10, but the conventional material of sample No. 12 can be used. Then it is impossible. In this way, using sample No. 10 makes it possible to increase the bolt span and reduce the number of cover mounting bolts.

Further, in the conventional rocker cover made of aluminum, the oil seal used for sealing the plug tube was press-fitted, but by using resin as the material, the oil seal can be welded to the rocker cover. . Further, according to the resin material of the present invention, it is possible to directly attach a heavy object such as an ignition plug coil, which has not been realized by the conventional resin.

In FIG. 4, curve 1 is the result of the molded product of sample No. 12 having a thickness (t) of 2.75 mm at 150 ° C., and curve 2 is a molded product of sample No. 10 having a thickness (t) of 2.5 mm. 150 ℃
As a result, the curve 3 is shown for reference, and shows the result at 25 ° C. of the molded product having the thickness (t) of 2.75 mm according to Sample No. 12.

[0047]

As described above, the polyamide composition used in the present invention has good moldability and excellent mechanical properties such as rigidity, elastic modulus at room temperature and high temperature, and tensile strength, and surface properties. It is possible to give a highly accurate molded product. Therefore, in the resin cover for an internal combustion engine formed by using such a material, the mounting flange, the bolt seat, and the general wall thickness can be reduced, and the cost and the weight can be reduced. Further, since it is possible to mount a heavy object such as an ignition coil of a plug, which has been impossible with a conventional resin material, the engine can be made compact. Also, because it has excellent vibration damping performance,
When used as a rocker cover, high quietness can be realized. Further, since the cover of the present invention has a significantly improved thermal deformation and warpage characteristics, the gasket seal flange can be made thinner, and further, the number of cover mounting bolts can be reduced, resulting in an effect that cost and weight can be reduced. .

[Brief description of drawings]

FIG. 1 (a) is a perspective view of a plate-shaped molded product formed from pellets of Test No. 1 of Test Example 1 when a warpage amount is measured, and (b) is a sample No. of Test Example 1 of FIG. FIG. 9 is a perspective view of a molded product when the warpage amount of the plate-shaped molded product molded from the pellet of No. 5 is measured.

FIG. 2 is a graph showing the relationship between the amount of glass fiber, the amount of mineral filler, and the amount of warpage of the molded products of Sample Nos. 9 to 12 of Test Example 2.

FIG. 3 is a graph showing the relationship between the amount of glass fiber, the amount of mineral filler, and the flexural modulus of the molded products of Sample Nos. 9 to 12 of Test Example 2.

FIG. 4 is a diagram showing the relationship between the amount of deformation between the flange span and the bolt span distance when the rocker covers using sample No. 10 and sample No. 12 of Test Example 2 are at high temperature.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C08L 77/00 KLC // B29K 77:00 (72) Inventor Ritsufumi Komatsu Kanagawa-ku, Yokohama 2 Takaramachi Nissan Motor Co., Ltd. (72) Inventor Toru Shinohara 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Nissan Motor Co., Ltd. (72) Ryuichi Hayashi 4997 Shinyoshida-cho, Kohoku-ku, Yokohama, Kanagawa Prefecture DuPont Japan Limited Central Research Institute

Claims (1)

[Claims] 1. A polyamide resin comprising 40 parts by weight of glass fiber and mineral filler in a total amount of 60 parts by weight, and the distribution thereof is 35 to 55 parts by weight of glass fiber and 5 to 25 parts by weight of mineral filler. Melted resin viscosity is 1216 s
A high-rigidity resin cover characterized by comprising a polyamide resin composition having a shear rate of ec ^-1 in the range of 50 to 200 Pascal seconds.