Method for producing a polyethylene naphthalate

A method for producing a polyethylene naphthalate, which comprises reacting

• (A) a naphthalenedicarboxylic acid comprising a naphthalenedicarboxylic acid represented by the following formula (I) as its main component;
• with
• (B) a glycol comprising ethylene glycol as its main component;
• in the presence of (a) at least one metal compound selected from the group consisting of glycol-soluble magnesium compounds, glycol-soluble manganese compounds, and glycol-soluble zinc compounds;
• (b) a nitrogen-containing basic compound;
• and (c) a phosphorous compound selected from the group consisting of triethylamine, tributylamine, dimethylaniline, pyridine, quinoline, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, triethylbenzylammonium hydroxide, 1,8-diazabicyclo(5;4,0)undecene;
• imidazole and its derivatives, and 1,4-biazacyclo(2,2,2)octane;
• and further in the presence of (d) a glycol-soluble germanium compound in the form of a solution in a glycol;
• the amount of the metal compound, the nitrogen-containing basic compound, the phosphorous compound, and the germanium compound being such that a relationship expressed by the following expressions is satisfied:
• formula (I) ##STR3## expressions
• 0. 005<M<1.0 (1)
• 0.00015<M/P<0.024 (2)
• 0.01<A/(M+G)<0.70 (3)
• 0.21<G<2.18 (4)
• wherein
• M:
• the amount of the magnesium, manganese, and zinc atoms to be added on the basis of the polymer (g atom/ton),
• P:
• the amount of the phosphorous atoms to be added on the basis of the polymer (ppm),
• A:
• the number of mols of the nitrogen-containing basic compound to be added on the basis of the polymer (mol/ton), and
• G:
• the amount of the germanium atoms to be added on the basis of the polymer (g atom/ton).