1. Field of the Invention
The present invention relates to a nigrosine granulated colorant that is used to impart a color to thermoplastic resin and for other purposes and has good handlability and good dispersibility in resin, a method of producing the same, a high-concentration master batch using the granulated colorant, a method of producing the same, and a colored composition using the granulated colorant or high-concentration master batch.
2. Description of the Prior Art
Because thermoplastic resins have excellent mechanical and chemical properties, they are widely used in plastic molding products in the field of components for automobiles, electric/electronic products and the like, and the demands are increasing in the field of engineering plastics. Additionally, thermoplastic resins are fitted to a broad range of industrial applications by formulating fibrous reinforcing material in thermoplastic resins to improve the heat resistance and chemical resistance, and to confer mechanical properties matching with various applications. In particular, in the field of automobiles, bicycles and the like, there has been a remarkable trend toward replacement of conventional metal parts with fiber-reinforced thermoplastic resin parts, for the purpose of weight reduction, manufacturing process rationalization and corrosion prevention.
Thermoplastic resins are colored for decoration, color identification, improvement of light fastness of molded products, content protection and shading and for other purposes, with black coloring being the most important in the industry. Traditionally, various inorganic pigments and organic dyes/pigments, such as carbon black, black metal complex dyes, nigrosine dyes and perinone black, have been used to impart a black color to thermoplastic resins. Of these, nigrosine dyes enable imparting vividly black colors with excellent appearance and surface gloss, and hence have been widely used to impart a color to thermoplastic resins with various attempts.
Specifically, such attempts include a molded blend wherein a polyamide resin is colored with carbon black and nigrosine (Japanese Patent Examined Publication No. SHO-60-43379), a glass fiber-reinforced black polyamide resin composition comprising a polyamide resin, a surface-treated glass fiber and an azine dye (Japanese Patent Laid-Open No. HEI-6-128479), a black polyamide resin composition wherein a polyamide resin is colored with a nigrosine dye, aniline black and carbon black (Japanese Patent Laid-Open No. HEI-9-255869), a polyester resin composition wherein a polyester resin is colored with a dye having a phenazine ring (nigrosine dye) (Japanese Patent Laid-Open No. HEI-10-292098), a colored thermoplastic resin composition wherein a crystalline resin (e.g., polyamide resin, polybutylene terephthalate resin, etc.) is colored with a modified nigrosine dye and related art (Domestic Re-publication of PCT International Publication No. WO00/26302).
Generally, in coloring a fiber-reinforced thermoplastic resin, a problem arises that the colorant (particularly black pigment) is difficult to sufficiently uniformly disperse in the resin even with a long time of kneading, because a fibrous reinforcing material is present in the resin. In particular, the spoilage of the gloss, appearance and the like of the colored molded product by the fibrous reinforcing material floating on the surface of the molded product during molding has been problematic. In this regard, there is room for improving colored resin compositions comprising a nigrosine dye.
Additionally, because nigrosine dyes are powders having small values of bulk density and average particle diameter, nigrosine dye dusting can occur during dye charge, blending with the resin, and the like, posing the problem with work environment deterioration, so that special measures have been required to prevent the dusting.
Furthermore, a master batch of nigrosine dye is produced by, for example, blending a resin and a dye in a mechanical mixer such as a Henschel mixer or blender, and extrusion-molding the blend using a single-screw extruder or twin-screw extruder into a resin pellet. In this manufacturing process, however, drawbacks, including phenomena such as bridging in the hopper and unsmooth feed of raw materials (resin, nigrosine dye, etc.) into the screw during extrusion kneading due to fluidity differences between nigrosine dye and resin, and a lack of fluidity due to dye wetting and adhesion as a result of dye exposure to the gas from the resin, additives and the like in the extrusion process, have been likely. As such, nigrosine dyes are extremely poorly handlable; it has been difficult to fill a nigrosine dye in a master batch at high concentrations.
The present invention has been developed in view of the aforementioned problems in the prior art, and is intended to provide a colorant that modifies the dusting of nigrosine dye, ensures good handlability in transportation, packaging, charge and the like, is unlikely to lose shape during the handling, and enables good and uniform dispersion of a nigrosine dye in a resin by blending or kneading with the resin in various forms of color imparting, including coloring a resin containing a fibrous reinforcing material and high-concentration resin coloring, a method of producing the same, a master batch that does not exhibit bridging or separation of a colorant from resin during blending or kneading said colorant with the resin during production and uniformly contains a high concentration of nigrosine dye, a method of producing the same, and a colored composition that uniformly contains a nigrosine dye, has a well controlled crystallization temperature with nigrosine dye, enables easier commercialization of products that must meet the rigorous demands for precision molding and dimensional accuracy, confers good appearance and surface gloss to molded products, has excellent light fastness, undergoes little color changes over time, and has good mechanical properties.