Biaxially oriented polyester film for lamination onto metal sheet

A biaxially oriented polyester film made of a polyester composition, which polyester composition consists essentially of:

• (a) an aromatic copoyester having a melting point of 220-235.degree. C.,
• (b) first inert fine solid particles having an average particle diameter of 0.08 to 0.5 .mu.m, and
• (c) second inert fine solid particles having an average particle diameter of 0.4 to 2.0 .mu.m,
• wherein said first inert fine solid particles and said second inert fine solid particles each have a sharp particle diameter distribution and a relative standard deviation of particle diameter of 0.5 or less and
• the ratio of the average particle diameter of the second inert fine solid particles to the average particle diameter of the first inert fine solid particles being at least 3.0, and the amounts of the components (b) and (c) being 0.10 to 1.0% by weight and 0.002 to 0.1% by weight, respectively, based on the total weight of the components (a), (b) and (c);
• and said film having a thickness of 10 to 75 .mu.m,
• wherein the polyester film has a plane orientation coefficient of 0.09 to 0.15 and has excellent moldability;
• which shows a deep drawability-(2) of 0.1 mA or less when laminated onto a metal sheet and subjected to deep drawing.

A biaxially oriented polyester film made of a polyester composition, which polyester composition consists essentially of:

• (a) an aromatic copolyester having a melting point of 210-245.degree. C.,
• (b) first inert fine solid particles having an average particle diameter of 0.05 to 0.6 .mu.m, and
• (c) second inert fine solid particles having an average particle diameter of 0.3 to 2.5 .mu.m,
• wherein said first inert fine solid particles and said second inert fine solid particles each have a sharp particle diameter distribution and a relative standard deviation of particle diameter of 0.5 or less and
• the ratio of the average particle diameter of the second inert fine solid particles to the average particle diameter of the first inert fine solid particles being at least 2.5, and the amounts of the components (b) and (c) being 0.01 to 3.0% by weight and 0.001 to 0.2 by weight, respectively, based on the total weight of the components (a), (b) and (c);
• wherein the polyester film has a plane orientation coefficient of 0.08 to 0.16 and has excellent moldability;
• which shows a deep drawability-(2) of 0.1 mA or less when laminated onto a metal sheet and subjected to deep drawing.