Inorganic reinforced polyamide resin compositions

There is disclosed an inorganic reinforced polyamide resin compositions obtainable by melt kneading of (A) a crystalline polyamide rein, (B) a semi-aromatic amorphous polyamide resin, and (C) an inorganic reinforcing material, wherein the relative viscosity of 96% sulfuric acid solution of the composition is 2.1 or lower and wherein the crystallization temperature (TC2) of the composition as measured with a temperature drop by differential scanning calorimetry (DSC) is 180&deg; C. or lower. The inorganic reinforced polyamide resin composition can provide shaped articles having satisfactory strength and rigidity without deteriorating their appearances and further having excellent coating properties and weathering resistance, and requires a mold temperature of 100&deg; C. or lower in the preparation of shaped articles.

FILED OF INVENTION

The present invention relates to inorganic reinforced polyamide resin compositions comprising crystalline polyamide resins, semi-aromatic amorphous polyamide resins, and inorganic reinforcing materials. More particularly, the present invention relates to inorganic reinforced polyamide resin compositions, which can provide shaped articles having satisfactory strength and rigidity without deteriorating their appearances (e.g., specular surface gloss, evenness of embossed surface) and further having excellent coating properties and weathering resistance, and which require a mold temperature of 100 C. or lower in the preparation of shaped articles. These inorganic reinforced polyamide resin compositions are suitable for automobile exterior parts, particularly door mirror parts.

BACKGROUND OF THE INVENTION

In general, polyamide resins have excellent mechanical characteristics, heat resistance, impact resistance, and chemical resistance; therefore they have been widely used for automobile parts, electrical appliance parts, electronic parts, domestic miscellaneous goods, and other various applications. Among these, polyamide resins reinforced with inorganic materials, typically glass fibers, have remarkably increased rigidity, strength, and heat resistance. In particular, it has been known that rigidity can be improved in proportion to the amounts of reinforcing materials added. However, if reinforcing materials such as glass fibers are added in large quantities, for example, in amounts of 50% to 70% by weight, to polyamide resins for the purpose of improving rigidity and strength, the polyamide resin compositions thus obtained provide shaped articles having extremely deteriorated appearances (e.g., specular surface gloss, evenness of embossed surface), resulting in a remarkable damage to the commercial value of these shaped articles.

Accordingly, for improving the appearances of shaped articles, there have been proposed many methods in which amorphous polyamide resins are added to crystalline polyamide resins (see, e.g., JP-A 2-140265, JP-A 3-9952, JP-A 3-269056, JP-A 4-202358).

These methods, however, cannot provide good specular surface gloss or even surface gloss of embossed surface. Further, there have been known methods for improving strength and rigidity by the addition of nylon-66, glass fibers, and mica in great amounts to semi-aromatic polyamide resins (MXD-6) (see, e.g., JP-A 1-263151). In this case, however, the temperature of a mold used in the preparation of shaped articles should be increased to high temperatures, for example, 135 C., or even if the mold temperature is increased to such high temperatures, the shaped articles thus obtained may sometimes have no good appearances.

SUMMARY OF THE INVENTION

Under these circumstances, the present inventors have extensively studied to develop a polyamide resin composition, which can provide shaped articles having satisfactory strength and rigidity without deteriorating their appearances and further having excellent coating properties and weathering resistance, and which requires a mold temperature of 100 C. or lower in the preparation of shaped articles, even if reinforcing materials such as glass fibers are added in large quantities, for example, in amounts of 50% by weight or higher, to polyamide resins for the purpose of improving strength and rigidity.

As a result, they have found that such a polyamide resin composition can be obtained by the combination of (A) a crystalline polyamide resin, (B) a semi-aromatic amorphous polyamide resin, and (C) an inorganic reinforcing material, and by the control of relative viscosity and crystallization temperature as measured with a temperature drop, of the composition after melt kneading of these ingredients, thereby completing the present invention.

Thus the present invention provides an inorganic reinforced polyamide resin composition obtainable by melt kneading of (A) a crystalline polyamide rein, (B) a semi-aromatic amorphous polyamide resin, and (C) an inorganic reinforcing material, wherein the relative viscosity of 96% sulfuric acid solution of the composition is 2.1 or lower and wherein the crystallization temperature (TC2) of the composition as measured with a temperature drop by differential scanning calorimetry (DSC) is 180 C. or lower.

EXAMPLE

The present invention will hereinafter be further illustrated by some examples; however, the present invention is not limited to these examples.

The characteristics and physical properties shown in the following Examples and Comparative Examples were determined by the test methods as described below (the contents of JIS standards and ASTM documents are incorporated herein by reference).

The relative viscosity was measured by 96% sulfuric acid solution according to JIS K 6810.

(2) Crystallization Temperature (TC2) as Measured with a Temperature Drop:

The crystallization temperature (TC2) as measured with a temperature drop was determined by differential scanning calorimetry (DSC) under a stream of nitrogen gas by increasing the temperature to 300 C. at a rate of 20 C./min., keeping a sample composition at that temperature for 5 minutes, and decreasing the temperature to 100 C. at a rate of 10 C./min.

The water content was measured according to JIS K 6810.

The melt flow index (MFI) was measured at 275 C. under a load of 2160 g according to JIS K 7210.

The tensile strength was measured according to ASTM D-638.

The tensile modulus of elasticity was measured according to ASTM D-638.

With a specularly-finished mold of 100 mm 100 mm in size and 3 mm in thickness, a shaped article was prepared at a resin temperature of 280 C. and at a mold temperature of 80 C., and then measured for gloss at an incident angle of 60 according to JIS Z 8714 (larger values indicate higher gloss).

The evaluation was carried out on the criteria: gloss values of 92 or higher: , gloss values of 91 to 75: , and gloss values of 74 or lower: X.

With an embossed, plate-shaped mold (a plan view thereof is shown in FIG. 1 , and the shaded area in FIG. 1 represents a portion of the mold, into which a resin is not introduced), molding was carried out at a resin temperature of 285 C. and at a mold temperature of 80 C. to prepare a shaped article of 2.5 mm in thickness, which was then evaluated for evenness of embossed surface by visual observation.

Criteria of evaluation:

mark: the transfer of an embossed pattern is good all over the surface and there is no uneven gloss;

mark: the transfer of an embossed pattern is different in part and there is slight uneven gloss;

X mark: the transfer of an embossed pattern is greatly different in part and there is remarkable uneven gloss, and such a shaped article cannot be used for exterior parts.

With a sunshine weatherometer (SWOM), testing was carried out at a panel temperature of 63 C., at a humidity of 50% RH, and at a spray cycle of irradiation for 120 minutes and rainfall for 18 minutes, and the specular gloss of a shaped article was measured after 500 hours of irradiation time.

The evaluation was carried out on the criteria: gloss values of 50 or higher: , gloss values of 49 to 30: , and gloss values of 29 or lower: X.

(10) Evaluation of Coating Adhesion:

Coating method: using a spray gun; coating thickness, about 30 m

Method of evaluation: according to JIS K 5400-1990 for adhesion strength

Initial coating adhesion: a shaped article after baking of a coating was left for one day, and then measured for adhesion strength and evaluated on the criteria described below.

Water-resistant coating adhesion: a shaped article after baking of a coating was left for one day, and then treated by immersion in warm water at 40 C. for 500 hours, and then measured for adhesion strength and evaluated on the criteria described below.

Comparative Examples 1-3

The ingredients (A), (B), and (C), and optionally, ingredients (E), (F), (G), and sebacic acid as a viscosity-reducing agent, and further, calcium montanate as a release agent in an amount of 0.4 part by weight, were mixed in each composition ratio shown in Table 1, and melt kneaded in a 35 double-screw extruder at a cylinder temperature of 270 C. and at a screw revolution speed of 70 rpm to give each inorganic reinforced polyamide resin composition, which was then extruded into pellets. The pellets thus obtained were dried in a hot-air dryer to a water content of 0.05% or lower, and then evaluated for various characteristics. The results of evaluation are shown in Table 1.

Comparative Examples 4-7

The ingredients (A), (B), and (C), and optionally, organic compounds shown in Table 2 as ingredient (D) and sebacic acid as a viscosity-reducing agent, and further, calcium montanate as a release agent in an amount of 0.4 part by weight, were mixed in each composition ratio shown in Tables 3, 4, and melt kneaded in a 35 double-screw extruder at a rein temperature of 260 C. to 300 C. and at a screw revolution speed of 40 to 60 rpm to give each inorganic reinforced polyamide resin composition, which was then extruded into pellets. The pellets thus obtained were dried in a hot-air dryer to a water content of 0.05% or lower, and then evaluated for various characteristics. The results of evaluation are shown in Tables 3 and 4.

TMD-T/6: a copolymer of trimethylhexamethylenediamine (TMD), terephthalic acid (T), and -caprolactam (6). The ratio of TMD-T/6 is 85/15 (weight ratio), and the relative viscosity thereof is 2.3.

glass fiber: RESO3-TP64T available from NIPPON GLASS FIBER CO., LTD.

As can be seen from Tables 1, 3, and 4, the inorganic reinforced polyamide resin compositions of the present invention provided shaped articles having excellent strength and rigidity as well as excellent appearances (i.e., specular surface gloss and evenness of embossed surface) and further having excellent coating properties and weathering resistance, and required a mold temperature of 100 C. or lower in the preparation of shaped articles.

The inorganic reinforced polyamide resin compositions of the present invention having such excellent performance can suitably be used as engineering plastics for automobiles, electrical appliance and electronic parts, and other various applications, and can therefore make a great contribution to the industrial world.