Phosphorus compounds have been broadly used for agricultural chemicals, plasticizing agents, flame retardants, metal extraction agents and the like, where the best of the specific characteristics thereof are brought out. Phosphorus compounds particularly have excellent functions as flame retardants, and are used in various synthetic resins, such as polyester, polycarbonate, ABS resins and polyurethane, and synthetic fibers, and the like. Phosphorus compounds cover a wide range of application.
Polyester fibers have excellent mechanical characteristics and easy processability, and thus, they have been used in various fields including clothes, interior, nonwoven fabrics, industrial materials and the like. In recent trends for increased awareness of disaster prevention, flame retardancy takes an important role in the use thereof for curtains, seats used in vehicles and the like, and the demand for flame-retardancy is increasing day by day.
For the past flame retardants for polyester fibers, halogen compounds have been mainly used with the most notable example of hexabromocyclododecane (HBCD). However, these compounds have been regulated more and more as being considered as substances having low degradability and high bioaccumulation potential. In addition, since products with flame proof finish will produce toxic hydrogen halide when being burned, development of safer flame retardants is desired. As a result, researches for phosphorus compounds not containing halogens are eagerly conducted for flame retardants for polyester fibers.
The following prior arts exist fora flame retardant for polyester fibers, consisting of a phosphorus compound that does not contain halogen, and a flame retarding method using the flame retardant.
Japanese Laid-Open Publication No. 2002-275473 (Patent Document 1) discloses a phosphorus compound having a dibenzoxaphosphorineoxide backbone, and both Japanese Laid-Open Publication No. 2000-328445 (Patent Document 2) and Japanese Laid-Open Publication No. 2003-27373 (Patent Document 3) disclose resorcinol bis-diphenylphosphate (RPD). While these compounds have high flame retardancy, they also have defects in their physical properties, such as light resistance, durability and stainability.
As a compound for overcoming such problems, Domestic Publication of PCT International Publication WO 2007/032277 (Patent Document 4) discloses 5,5-dimethyl-2-(2′-phenylphenoxy)-1,3,2-dioxaphosphorin ane-2-oxide as a phosphorus compound. This compound is excellent in hydrolysis resistance and heat resistance, and thus, the compound has excellent preservation stability when used as a flame proof finish agent, and it can provide high flame retardancy without reducing the physical properties of resin or fiber. The compound also has high adherence and exhaustion properties to polyester fibers and does not prevent a dye from adhering to the fibers. Thus, the compound is an extremely excellent phosphorus compound which allows fibers after flame retardant dying treatment to have excellent light resistance, durability and rubbing fastness.
For the method for synthesizing the compounds described above, the following method is generally known.
Patent Document 4 describes a synthesizing method, in which a phenol compound or naphthol compound, which may be substituted with di-substituted phosphorohalidate, are allowed to react in the presence of triethylamine as a hydrogen halide scavenger, and, if needed, a Lewis acid catalyst such as magnesium chloride, to synthesize a corresponding phosphate.
However, with this method, it is difficult to perform synthesis with favorable purity, and the method requires recrystallization to increase the purity. Furthermore, since an expensive amine compound, such as triethylamine, tributylamine or pyridine, is used as a hydrogen halide scavenger, the raw material cost drastically increases. Furthermore, since hydrogen halide salt of the amine compound is produced as a by-product during the reaction, causing the stirring effect to decrease, a larger amount of a reaction solvent is necessary. Furthermore, filtration and water treatment are known as publicly known techniques for removing hydrogen halide salt of the amine compound after capturing the hydrogen halide. However, through filtration, a large amount of the objective substance, i.e., phosphoric acid ester, will remain in the hydrogen halide salt of the amine compound, and the device for handling the filtration will be large-scale. Thus, water treatment is considered for industrial purposes. However, a large amount of water will be required for the water treatment, which greatly reduces the capacity efficiency in the production. Moreover, since the water layer during the removal of hydrogen halide salt of the amine compound contains a large amount of organic amine salt, the product is likely to be contaminatedby organic material, which will cause reduction in the yield. Moreover, in the step of recovering amine from amine salt water, a large amount of strong alkali aqueous solution, such as sodium hydroxide or potassium hydroxide, is required to isolate amines, which will further increase the cost. Furthermore, the aqueous solution after recovering the amine has high concentration of alkali metal salt, and it is difficult for ordinary facilities to perform waste water treatment due to a small amount of remaining amine. Furthermore, the amine after being recovered contains water, which will require dehydrating, distilling or other steps.
As described above, the use of an amine compound for reaction has the defects of, not only causing the increase in the raw material cost, but also requiring auxiliaries or the like for recovery and purification. Furthermore, water containing high concentration of hydrogen halide salt of the amine compound cannot be disposed of through ordinary methods from the environmental point of view, and thus, a special treatment will be necessary for the waste water treatment. As such, from the cost, facilities, labor and various other points of view, it is extremely disadvantageous to apply reactions using an amine compound for industrial purposes.