FLAME RESISTANT POLYAMIDE RESIN COMPOSITION

AND PROCESS FOR MANUFACTURE THEREOF

FIELD OF THE INVENTION

The present invention relates to a flame resistant polyamide resin composition which has flame resistance, as well as excellent mechanical properties, particularly a mechanical property such as a tensile at the break and elongation, or the like, and a process for the manufacture thereof.

DESCRIPTION OF THE RELATED ART

Because of their excellent mechanical properties, electrical properties, chemical resistance, and the like, polyamide resins are used in various fields such as electrical electronic parts but they are deficient, in general, in flammability for which studies have heretofore been carried out to obtain flame resistant polyamide resins. Methods have previously been used to achieve a flame resistant polyamide resin composition into which are compounded a variety of flame retarders, such as halogen compounds, phosphorus compounds, and the like; in particular, polyamide resin compositions compounded with a melamine cyanurate are known (Japanese Patent Laid Open S53-31759) to provide molded articles with good appearance without generating toxic components on thermal decomposition.

PROBLEMSTOBESOLVEDBYTHEINVENTION

The amount of the melamine cyanurates compounded for improving the flame resistance by such melamine cyanurate incorporation are, in general. 5-10% by weight, wherein the greater the amount compounded, the greater the flame resistance. However, when compounded in a large amount, the dispersibility of the melamine cyanurate in the polyamide resin is poorer, so that the flame resistant polyamide resin composition in which such a flame retardant is compounded is inferior in mechanical properties

compared with those having no such flame retardant. Therefore, it has been desired to improve mechanical properties, such as tensile elongation, and the like, in particular in electrical and electronic parts applications.

There exists a method known to improve the state of dispersion of the melamine cyanurate in the polyamide resin thereby preventing its mechanical properties from decreasing, in which the melamine cyanurate is surface coated to prevent its aggregation. See, for example, Japanese Patent Laid Open H6- 157820. However, this method is deficient in that costs are relatively high and the coated melamine cyanurate blooms out to the surface of the shaped article and adversely affects the flame resistance.

In view of the above situation, it is an objective of this invention to provide a flame resistant polyamide resin composition having improved mechanical properties, in particular tensile at the break and elongation, and a process for the manufacture thereof.

SUMMARY OF THE INVENTION

The present invention relates to a flame resistant polyamide resin composition obtained by melt-kneading a polyamide resin with a masterbatch obtained by melt-kneading a polyamide resin and a melamine cyanurate, wherein the content of the melamine cyanurate in the composition is 1-30% by weight.

The invention also relates to a process for manufacturing a flame resistant polyamide resin composition by melt-kneading a polyamide resin with a melamine cyanurate into a masterbatch and a step of further melt-kneading the masterbatch with a polyamide resin into the composition.

DETAILED DESCRIPTION

The means for solving the problems mentioned above are set forth below.

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Embodiment 1 of this invention is a flame resistant polyamide resin composition comprising a composition obtained by melt- kneading a polyamide resin with a masterbatch obtained by melt- kneading a polyamide resin and a melamine cyanurate, wherein the content of the melamine cyanurate in the composition is 1-30% by weight.

Embodiment 2 of this invention is a flame resistant polyamide resin composition in embodiment 1 where the content of the melamine cyanurate in the masterbatch is 10-60% by weight.

Embodiment 3 of this invention is a process for the manufacture of a flame resistant polyamide resin composition which comprises a step of melt-kneading a polyamide resin with a melamine cyanurate into a masterbatch and a step of further melt- kneading the masterbatch with a polyamide resin into the composition.

Embodiment 4 of this invention is a process for the manufacture of a flame resistant polyamide resin composition in embodiment 3 wherein the content of the melamine cyanurate in the masterbatch is 10-60% by weight.

The present invention is now specifically described below.

Polyamide resins which are used in this invention include polymers obtained by polycondensing diamines, such as hexamethylene diamine and a dicarboxylic acid, such as terephthalic acid, isophthalic acid, and adipic acid; polymers from epsilon-caprolactam, amino caproic acid, enantho lactam, 7-aminoheptanoic acid, alpha-pyrrolidone, and copolymers thereof. Specifically, use may be made of a single known polyamide resin, such as nylon 66 or nylon 6, a blend of a plurality of resins, or copolymers thereof, preferably nylon 66 and/or nylon 6.

The melamine cyanurate which is used in this invention is an equimolar reaction product of cyanuric acid and a melamine, for

example, obtained by mixing an aqueous cyanuric acid and an aqueous melamine solution with agitation to allow reaction to take place at a temperature of about 90-100°C, and filtering the precipitate generated. The melamine cyanurate is, in general, a white solid which may be reduced to a fine powder or a commercial powdery product may be used as obtained or after pulverization. The melamine cyanurate used in this invention may have some of its amino or hydroxyl groups substituted with other substituents and the term "melamine cyanurate" referred to in this invention shall include such substituted versions as well.

Such melamine cyanurate is preferably contained in this invention in an amount of 1-30% by weight in the final polyamide composition. An amount less than this range can no longer provide the expected flame retardation effect, while an amount exceeding this range will reveal an adverse effect on the mechanical properties, thus making both extremes undesirable.

The flame retardant polyamide resin composition of this invention is obtained by first melt kneading the above melamine cyanurate with a polyamide resin, followed by melt kneading the masterbatch with an additional polyamide resin. In other words, the flame resistant polyamide composition of this invention has a melamine cyanurate kneaded-in a total of two times, initially at a high concentration and then at a relatively low concentration, to make the dispersion of the melamine cyanurate in the polyamide resin very good. This enables the final product to obtain excellent flame resistance characteristics without reducing the mechanical properties, particularly resulting in suitable products to be used in applications in electrical and electronic parts, and the like.

The masterbatch of the composition of this invention is, for example, obtained by kneading 10-60% by weight, preferably 30- 40% by weight of a melamine cyanurate with a polyamide resin. An amount of the melamine cyanurate below this range will not give any advantage of using a masterbatch, while an amount exceeding this range will cause manufacturing problems, such as a difficulty in dispersion and the occurrence of strand breakage

during manufacturing. In addition, it will have a tendency to show reduced mechanical properties. Such a masterbatch may be compounded with additives, such as a dispersion agent, a heat stabilizer, an antiweathering agent, a slip agent, a colorant, a filler. an antistatic agent, or the like.

In the manufacture of such a masterbatch, the melamine cyanurate may be pre-blended with the polyamide or else may be separately fed to the extruder from independent hoppers, or else from a side feeder, either of which may be used in combination, but the consideration of workability and safe feeding makes it preferable to feed from a side feeder. The kneading is carried out using an extruder, or the like, at a temperature at which the polyamide resin used melts.

The masterbatch thus manufactured is then further uniformly mixed with a polyamide resin for melt-kneading to give a flame resistant polyamide composition. The aforementioned additives may be added at this stage or may be added at this stage additionally to a masterbatch to which some additives have already been added. There is no particular limitation as to the method of manufacture as well, as long as a uniform and final melt kneading can be carried out.

The compounding ratio of the masterbatch and the polyamide resin should be one to be within the above range for the compounding ratio of the melamine cyanurate. The polyamide resin used here may not necessarily be the same polyamide resin which is compounded in the masterbatch, as long as it can give finally a uniform flame resistant polyamide resin composition.

The flame resistant polyamide resin composition of this invention has the melamine cyanurate as described above obtained by a two-step kneading for it to be compounded in the polyamide resin so that it provides good dispersibility even at a high compounding level of the melamine cyanurate, so as to give a flame resistant polyamide resin composition having good mechanical properties.

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Therefore, in the manufacture of a flame resistant polyamide resin composition containing a melamine cyanurate, the use of a method of first kneading a melamine cyanurate initially at a high concentration into a polyamide resin followed by kneading with an additional polyamide resin can give a polyamide resin composition which has good mechanical properties and excellent flame resistance.

EXAMPLES

The present invention is now described by the following examples where the invention is not limited to these examples given below:

Examples 1-4

While nylon 66 was kneaded in a twin screw extruder (manufactured by W&P Company, ZSK-40) melamine cyanurate (MC) was side fed to reach a content of 30-32% by weight to give masterbatch pellets shown below. Each masterbatch was melt-kneaded with nylon 66, to reach the final MC concentration to a level given below, by a twin screw extruder (manufactured by W&P Company, ZSK-40) to give flame resistant polyamide resin compositions. They were molded by an injection molder (manufactured by Sumitomo Nestarl ) into test pieces.

Nylon 66: Zytel® resin manufactured by the DuPont Company.

Melamine Cyanurate: MC440, manufactured by Nissan Kagaku Company.

Flammability and mechanical properties were measured on each test piece as given below with the results listed in Table 1. Measurements were made according to ASTM D-638-58T for elongation, ASTM D-638 for tensile strength, and ASTM D-256 for

notched Izod impact strength. Flammability was measured using a 1/32 inch (about 0.8 mm) test piece according to UL94.

Comparative Examples 1-3

Nylon 66 and melamine cyanurate, similar to those used in the above examples, were preblended for ten minutes by a Henschel mixer to bring the melamine cyanurate content to 5, 8, and 9% by weight, followed by melt kneading each blend further by a twin screw extruder (manufactured by W&P Company, ZSK-40) into pellets. Each pelletized product was molded by an injection molder (Sumitomo Nestarl [Phonetic Translation]) into test pieces on which elongation and flammability were measured in a manner similar to that of the above examples. These results are also given in Table 1.

TABLE 1

Masterbatch MC MC Elongation Flammability Tensile Notched Izod Concentration Concentration (%) Strength Impact Strength in the Final (MPa) (J/m)

Composition

Examples

1 30% by weight 5% by weight 16.9 V-O 92.0 29.4

2 32% by weight 8% by weight 13.3 V-O 88.1 30.4

3 30% by weight 9% by weight 12.4 V-O 87.6 41.2 I

4 30% by weight 1 1% by weight 1 1.0 V-O 87.0 35.9 0

Comparative Examples

1 (Preblended) 5% by weight 12.5 V-O 89.7 43.9

2 (Preblended) 8%o by weight 10.1 V-O 79.0 32.5

3 (Preblended) 9% by weight 6.7 V-O 87.3 30.0

It was confirmed by the above results that molded articles obtained from compositions of Examples 1-4 of this invention give substantially better elongations compared to the Comparative Examples containing the same concentrations of MC. As the MC concentration reaches as high as 9% by weight in the usual kneading, the dispersibility of the MC rapidly decreases, causing the mechanical properties of the molded articles to drop precipitously , but it became clear that the examples of this invention showed no abrupt decrease in mechanical properties even when the MC concentration exceeded 10% by weight.

Advantageous Effect of the Invention

As described above, the present invention which generates a polyamide resin composition by kneading melamine cyanurate into a polyamide resin in two steps, so that the dispersibility of the melamine cyanurate is good, gives a molded article from such a composition that retains good mechanical properties with improved flame resistance, which is particularly good for use in electrical and electronic parts.